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4 | RFC 821 | |
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10 | SIMPLE MAIL TRANSFER PROTOCOL | |
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14 | Jonathan B. Postel | |
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44 | August 1982 | |
45 | ||
46 | ||
47 | ||
48 | Information Sciences Institute | |
49 | University of Southern California | |
50 | 4676 Admiralty Way | |
51 | Marina del Rey, California 90291 | |
52 | ||
53 | (213) 822-1511 | |
54 | \f | |
55 | \f | |
56 | ||
57 | ||
58 | RFC 821 August 1982 | |
59 | Simple Mail Transfer Protocol | |
60 | ||
61 | ||
62 | ||
63 | TABLE OF CONTENTS | |
64 | ||
65 | 1. INTRODUCTION .................................................. 1 | |
66 | ||
67 | 2. THE SMTP MODEL ................................................ 2 | |
68 | ||
69 | 3. THE SMTP PROCEDURE ............................................ 4 | |
70 | ||
71 | 3.1. Mail ..................................................... 4 | |
72 | 3.2. Forwarding ............................................... 7 | |
73 | 3.3. Verifying and Expanding .................................. 8 | |
74 | 3.4. Sending and Mailing ..................................... 11 | |
75 | 3.5. Opening and Closing ..................................... 13 | |
76 | 3.6. Relaying ................................................ 14 | |
77 | 3.7. Domains ................................................. 17 | |
78 | 3.8. Changing Roles .......................................... 18 | |
79 | ||
80 | 4. THE SMTP SPECIFICATIONS ...................................... 19 | |
81 | ||
82 | 4.1. SMTP Commands ........................................... 19 | |
83 | 4.1.1. Command Semantics ..................................... 19 | |
84 | 4.1.2. Command Syntax ........................................ 27 | |
85 | 4.2. SMTP Replies ............................................ 34 | |
86 | 4.2.1. Reply Codes by Function Group ......................... 35 | |
87 | 4.2.2. Reply Codes in Numeric Order .......................... 36 | |
88 | 4.3. Sequencing of Commands and Replies ...................... 37 | |
89 | 4.4. State Diagrams .......................................... 39 | |
90 | 4.5. Details ................................................. 41 | |
91 | 4.5.1. Minimum Implementation ................................ 41 | |
92 | 4.5.2. Transparency .......................................... 41 | |
93 | 4.5.3. Sizes ................................................. 42 | |
94 | ||
95 | APPENDIX A: TCP ................................................. 44 | |
96 | APPENDIX B: NCP ................................................. 45 | |
97 | APPENDIX C: NITS ................................................ 46 | |
98 | APPENDIX D: X.25 ................................................ 47 | |
99 | APPENDIX E: Theory of Reply Codes ............................... 48 | |
100 | APPENDIX F: Scenarios ........................................... 51 | |
101 | ||
102 | GLOSSARY ......................................................... 64 | |
103 | ||
104 | REFERENCES ....................................................... 67 | |
105 | \f | |
106 | \f | |
107 | ||
108 | ||
109 | Network Working Group J. Postel | |
110 | Request for Comments: DRAFT ISI | |
111 | Replaces: RFC 788, 780, 772 August 1982 | |
112 | ||
113 | SIMPLE MAIL TRANSFER PROTOCOL | |
114 | ||
115 | ||
116 | 1. INTRODUCTION | |
117 | ||
118 | The objective of Simple Mail Transfer Protocol (SMTP) is to transfer | |
119 | mail reliably and efficiently. | |
120 | ||
121 | SMTP is independent of the particular transmission subsystem and | |
122 | requires only a reliable ordered data stream channel. Appendices A, | |
123 | B, C, and D describe the use of SMTP with various transport services. | |
124 | A Glossary provides the definitions of terms as used in this | |
125 | document. | |
126 | ||
127 | An important feature of SMTP is its capability to relay mail across | |
128 | transport service environments. A transport service provides an | |
129 | interprocess communication environment (IPCE). An IPCE may cover one | |
130 | network, several networks, or a subset of a network. It is important | |
131 | to realize that transport systems (or IPCEs) are not one-to-one with | |
132 | networks. A process can communicate directly with another process | |
133 | through any mutually known IPCE. Mail is an application or use of | |
134 | interprocess communication. Mail can be communicated between | |
135 | processes in different IPCEs by relaying through a process connected | |
136 | to two (or more) IPCEs. More specifically, mail can be relayed | |
137 | between hosts on different transport systems by a host on both | |
138 | transport systems. | |
139 | ||
140 | ||
141 | ||
142 | ||
143 | ||
144 | ||
145 | ||
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147 | ||
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153 | ||
154 | ||
155 | ||
156 | ||
157 | ||
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159 | ||
160 | ||
161 | ||
162 | ||
163 | Postel [Page 1] | |
164 | \f | |
165 | ||
166 | ||
167 | August 1982 RFC 821 | |
168 | Simple Mail Transfer Protocol | |
169 | ||
170 | ||
171 | ||
172 | 2. THE SMTP MODEL | |
173 | ||
174 | The SMTP design is based on the following model of communication: as | |
175 | the result of a user mail request, the sender-SMTP establishes a | |
176 | two-way transmission channel to a receiver-SMTP. The receiver-SMTP | |
177 | may be either the ultimate destination or an intermediate. SMTP | |
178 | commands are generated by the sender-SMTP and sent to the | |
179 | receiver-SMTP. SMTP replies are sent from the receiver-SMTP to the | |
180 | sender-SMTP in response to the commands. | |
181 | ||
182 | Once the transmission channel is established, the SMTP-sender sends a | |
183 | MAIL command indicating the sender of the mail. If the SMTP-receiver | |
184 | can accept mail it responds with an OK reply. The SMTP-sender then | |
185 | sends a RCPT command identifying a recipient of the mail. If the | |
186 | SMTP-receiver can accept mail for that recipient it responds with an | |
187 | OK reply; if not, it responds with a reply rejecting that recipient | |
188 | (but not the whole mail transaction). The SMTP-sender and | |
189 | SMTP-receiver may negotiate several recipients. When the recipients | |
190 | have been negotiated the SMTP-sender sends the mail data, terminating | |
191 | with a special sequence. If the SMTP-receiver successfully processes | |
192 | the mail data it responds with an OK reply. The dialog is purposely | |
193 | lock-step, one-at-a-time. | |
194 | ||
195 | ------------------------------------------------------------- | |
196 | ||
197 | ||
198 | +----------+ +----------+ | |
199 | +------+ | | | | | |
200 | | User |<-->| | SMTP | | | |
201 | +------+ | Sender- |Commands/Replies| Receiver-| | |
202 | +------+ | SMTP |<-------------->| SMTP | +------+ | |
203 | | File |<-->| | and Mail | |<-->| File | | |
204 | |System| | | | | |System| | |
205 | +------+ +----------+ +----------+ +------+ | |
206 | ||
207 | ||
208 | Sender-SMTP Receiver-SMTP | |
209 | ||
210 | Model for SMTP Use | |
211 | ||
212 | Figure 1 | |
213 | ||
214 | ------------------------------------------------------------- | |
215 | ||
216 | The SMTP provides mechanisms for the transmission of mail; directly | |
217 | from the sending user's host to the receiving user's host when the | |
218 | ||
219 | ||
220 | ||
221 | [Page 2] Postel | |
222 | \f | |
223 | ||
224 | ||
225 | RFC 821 August 1982 | |
226 | Simple Mail Transfer Protocol | |
227 | ||
228 | ||
229 | ||
230 | two host are connected to the same transport service, or via one or | |
231 | more relay SMTP-servers when the source and destination hosts are not | |
232 | connected to the same transport service. | |
233 | ||
234 | To be able to provide the relay capability the SMTP-server must be | |
235 | supplied with the name of the ultimate destination host as well as | |
236 | the destination mailbox name. | |
237 | ||
238 | The argument to the MAIL command is a reverse-path, which specifies | |
239 | who the mail is from. The argument to the RCPT command is a | |
240 | forward-path, which specifies who the mail is to. The forward-path | |
241 | is a source route, while the reverse-path is a return route (which | |
242 | may be used to return a message to the sender when an error occurs | |
243 | with a relayed message). | |
244 | ||
245 | When the same message is sent to multiple recipients the SMTP | |
246 | encourages the transmission of only one copy of the data for all the | |
247 | recipients at the same destination host. | |
248 | ||
249 | The mail commands and replies have a rigid syntax. Replies also have | |
250 | a numeric code. In the following, examples appear which use actual | |
251 | commands and replies. The complete lists of commands and replies | |
252 | appears in Section 4 on specifications. | |
253 | ||
254 | Commands and replies are not case sensitive. That is, a command or | |
255 | reply word may be upper case, lower case, or any mixture of upper and | |
256 | lower case. Note that this is not true of mailbox user names. For | |
257 | some hosts the user name is case sensitive, and SMTP implementations | |
258 | must take case to preserve the case of user names as they appear in | |
259 | mailbox arguments. Host names are not case sensitive. | |
260 | ||
261 | Commands and replies are composed of characters from the ASCII | |
262 | character set [1]. When the transport service provides an 8-bit byte | |
263 | (octet) transmission channel, each 7-bit character is transmitted | |
264 | right justified in an octet with the high order bit cleared to zero. | |
265 | ||
266 | When specifying the general form of a command or reply, an argument | |
267 | (or special symbol) will be denoted by a meta-linguistic variable (or | |
268 | constant), for example, "<string>" or "<reverse-path>". Here the | |
269 | angle brackets indicate these are meta-linguistic variables. | |
270 | However, some arguments use the angle brackets literally. For | |
271 | example, an actual reverse-path is enclosed in angle brackets, i.e., | |
272 | "<John.Smith@USC-ISI.ARPA>" is an instance of <reverse-path> (the | |
273 | angle brackets are actually transmitted in the command or reply). | |
274 | ||
275 | ||
276 | ||
277 | ||
278 | ||
279 | Postel [Page 3] | |
280 | \f | |
281 | ||
282 | ||
283 | August 1982 RFC 821 | |
284 | Simple Mail Transfer Protocol | |
285 | ||
286 | ||
287 | ||
288 | 3. THE SMTP PROCEDURES | |
289 | ||
290 | This section presents the procedures used in SMTP in several parts. | |
291 | First comes the basic mail procedure defined as a mail transaction. | |
292 | Following this are descriptions of forwarding mail, verifying mailbox | |
293 | names and expanding mailing lists, sending to terminals instead of or | |
294 | in combination with mailboxes, and the opening and closing exchanges. | |
295 | At the end of this section are comments on relaying, a note on mail | |
296 | domains, and a discussion of changing roles. Throughout this section | |
297 | are examples of partial command and reply sequences, several complete | |
298 | scenarios are presented in Appendix F. | |
299 | ||
300 | 3.1. MAIL | |
301 | ||
302 | There are three steps to SMTP mail transactions. The transaction | |
303 | is started with a MAIL command which gives the sender | |
304 | identification. A series of one or more RCPT commands follows | |
305 | giving the receiver information. Then a DATA command gives the | |
306 | mail data. And finally, the end of mail data indicator confirms | |
307 | the transaction. | |
308 | ||
309 | The first step in the procedure is the MAIL command. The | |
310 | <reverse-path> contains the source mailbox. | |
311 | ||
312 | MAIL <SP> FROM:<reverse-path> <CRLF> | |
313 | ||
314 | This command tells the SMTP-receiver that a new mail | |
315 | transaction is starting and to reset all its state tables and | |
316 | buffers, including any recipients or mail data. It gives the | |
317 | reverse-path which can be used to report errors. If accepted, | |
318 | the receiver-SMTP returns a 250 OK reply. | |
319 | ||
320 | The <reverse-path> can contain more than just a mailbox. The | |
321 | <reverse-path> is a reverse source routing list of hosts and | |
322 | source mailbox. The first host in the <reverse-path> should be | |
323 | the host sending this command. | |
324 | ||
325 | The second step in the procedure is the RCPT command. | |
326 | ||
327 | RCPT <SP> TO:<forward-path> <CRLF> | |
328 | ||
329 | This command gives a forward-path identifying one recipient. | |
330 | If accepted, the receiver-SMTP returns a 250 OK reply, and | |
331 | stores the forward-path. If the recipient is unknown the | |
332 | receiver-SMTP returns a 550 Failure reply. This second step of | |
333 | the procedure can be repeated any number of times. | |
334 | ||
335 | ||
336 | ||
337 | [Page 4] Postel | |
338 | \f | |
339 | ||
340 | ||
341 | RFC 821 August 1982 | |
342 | Simple Mail Transfer Protocol | |
343 | ||
344 | ||
345 | ||
346 | The <forward-path> can contain more than just a mailbox. The | |
347 | <forward-path> is a source routing list of hosts and the | |
348 | destination mailbox. The first host in the <forward-path> | |
349 | should be the host receiving this command. | |
350 | ||
351 | The third step in the procedure is the DATA command. | |
352 | ||
353 | DATA <CRLF> | |
354 | ||
355 | If accepted, the receiver-SMTP returns a 354 Intermediate reply | |
356 | and considers all succeeding lines to be the message text. | |
357 | When the end of text is received and stored the SMTP-receiver | |
358 | sends a 250 OK reply. | |
359 | ||
360 | Since the mail data is sent on the transmission channel the end | |
361 | of the mail data must be indicated so that the command and | |
362 | reply dialog can be resumed. SMTP indicates the end of the | |
363 | mail data by sending a line containing only a period. A | |
364 | transparency procedure is used to prevent this from interfering | |
365 | with the user's text (see Section 4.5.2). | |
366 | ||
367 | Please note that the mail data includes the memo header | |
368 | items such as Date, Subject, To, Cc, From [2]. | |
369 | ||
370 | The end of mail data indicator also confirms the mail | |
371 | transaction and tells the receiver-SMTP to now process the | |
372 | stored recipients and mail data. If accepted, the | |
373 | receiver-SMTP returns a 250 OK reply. The DATA command should | |
374 | fail only if the mail transaction was incomplete (for example, | |
375 | no recipients), or if resources are not available. | |
376 | ||
377 | The above procedure is an example of a mail transaction. These | |
378 | commands must be used only in the order discussed above. | |
379 | Example 1 (below) illustrates the use of these commands in a mail | |
380 | transaction. | |
381 | ||
382 | ||
383 | ||
384 | ||
385 | ||
386 | ||
387 | ||
388 | ||
389 | ||
390 | ||
391 | ||
392 | ||
393 | ||
394 | ||
395 | Postel [Page 5] | |
396 | \f | |
397 | ||
398 | ||
399 | August 1982 RFC 821 | |
400 | Simple Mail Transfer Protocol | |
401 | ||
402 | ||
403 | ||
404 | ------------------------------------------------------------- | |
405 | ||
406 | Example of the SMTP Procedure | |
407 | ||
408 | This SMTP example shows mail sent by Smith at host Alpha.ARPA, | |
409 | to Jones, Green, and Brown at host Beta.ARPA. Here we assume | |
410 | that host Alpha contacts host Beta directly. | |
411 | ||
412 | S: MAIL FROM:<Smith@Alpha.ARPA> | |
413 | R: 250 OK | |
414 | ||
415 | S: RCPT TO:<Jones@Beta.ARPA> | |
416 | R: 250 OK | |
417 | ||
418 | S: RCPT TO:<Green@Beta.ARPA> | |
419 | R: 550 No such user here | |
420 | ||
421 | S: RCPT TO:<Brown@Beta.ARPA> | |
422 | R: 250 OK | |
423 | ||
424 | S: DATA | |
425 | R: 354 Start mail input; end with <CRLF>.<CRLF> | |
426 | S: Blah blah blah... | |
427 | S: ...etc. etc. etc. | |
428 | S: <CRLF>.<CRLF> | |
429 | R: 250 OK | |
430 | ||
431 | The mail has now been accepted for Jones and Brown. Green did | |
432 | not have a mailbox at host Beta. | |
433 | ||
434 | Example 1 | |
435 | ||
436 | ------------------------------------------------------------- | |
437 | ||
438 | ||
439 | ||
440 | ||
441 | ||
442 | ||
443 | ||
444 | ||
445 | ||
446 | ||
447 | ||
448 | ||
449 | ||
450 | ||
451 | ||
452 | ||
453 | [Page 6] Postel | |
454 | \f | |
455 | ||
456 | ||
457 | RFC 821 August 1982 | |
458 | Simple Mail Transfer Protocol | |
459 | ||
460 | ||
461 | ||
462 | 3.2. FORWARDING | |
463 | ||
464 | There are some cases where the destination information in the | |
465 | <forward-path> is incorrect, but the receiver-SMTP knows the | |
466 | correct destination. In such cases, one of the following replies | |
467 | should be used to allow the sender to contact the correct | |
468 | destination. | |
469 | ||
470 | 251 User not local; will forward to <forward-path> | |
471 | ||
472 | This reply indicates that the receiver-SMTP knows the user's | |
473 | mailbox is on another host and indicates the correct | |
474 | forward-path to use in the future. Note that either the | |
475 | host or user or both may be different. The receiver takes | |
476 | responsibility for delivering the message. | |
477 | ||
478 | 551 User not local; please try <forward-path> | |
479 | ||
480 | This reply indicates that the receiver-SMTP knows the user's | |
481 | mailbox is on another host and indicates the correct | |
482 | forward-path to use. Note that either the host or user or | |
483 | both may be different. The receiver refuses to accept mail | |
484 | for this user, and the sender must either redirect the mail | |
485 | according to the information provided or return an error | |
486 | response to the originating user. | |
487 | ||
488 | Example 2 illustrates the use of these responses. | |
489 | ||
490 | ------------------------------------------------------------- | |
491 | ||
492 | Example of Forwarding | |
493 | ||
494 | Either | |
495 | ||
496 | S: RCPT TO:<Postel@USC-ISI.ARPA> | |
497 | R: 251 User not local; will forward to <Postel@USC-ISIF.ARPA> | |
498 | ||
499 | Or | |
500 | ||
501 | S: RCPT TO:<Paul@USC-ISIB.ARPA> | |
502 | R: 551 User not local; please try <Mockapetris@USC-ISIF.ARPA> | |
503 | ||
504 | Example 2 | |
505 | ||
506 | ------------------------------------------------------------- | |
507 | ||
508 | ||
509 | ||
510 | ||
511 | Postel [Page 7] | |
512 | \f | |
513 | ||
514 | ||
515 | August 1982 RFC 821 | |
516 | Simple Mail Transfer Protocol | |
517 | ||
518 | ||
519 | ||
520 | 3.3. VERIFYING AND EXPANDING | |
521 | ||
522 | SMTP provides as additional features, commands to verify a user | |
523 | name or expand a mailing list. This is done with the VRFY and | |
524 | EXPN commands, which have character string arguments. For the | |
525 | VRFY command, the string is a user name, and the response may | |
526 | include the full name of the user and must include the mailbox of | |
527 | the user. For the EXPN command, the string identifies a mailing | |
528 | list, and the multiline response may include the full name of the | |
529 | users and must give the mailboxes on the mailing list. | |
530 | ||
531 | "User name" is a fuzzy term and used purposely. If a host | |
532 | implements the VRFY or EXPN commands then at least local mailboxes | |
533 | must be recognized as "user names". If a host chooses to | |
534 | recognize other strings as "user names" that is allowed. | |
535 | ||
536 | In some hosts the distinction between a mailing list and an alias | |
537 | for a single mailbox is a bit fuzzy, since a common data structure | |
538 | may hold both types of entries, and it is possible to have mailing | |
539 | lists of one mailbox. If a request is made to verify a mailing | |
540 | list a positive response can be given if on receipt of a message | |
541 | so addressed it will be delivered to everyone on the list, | |
542 | otherwise an error should be reported (e.g., "550 That is a | |
543 | mailing list, not a user"). If a request is made to expand a user | |
544 | name a positive response can be formed by returning a list | |
545 | containing one name, or an error can be reported (e.g., "550 That | |
546 | is a user name, not a mailing list"). | |
547 | ||
548 | In the case of a multiline reply (normal for EXPN) exactly one | |
549 | mailbox is to be specified on each line of the reply. In the case | |
550 | of an ambiguous request, for example, "VRFY Smith", where there | |
551 | are two Smith's the response must be "553 User ambiguous". | |
552 | ||
553 | The case of verifying a user name is straightforward as shown in | |
554 | example 3. | |
555 | ||
556 | ||
557 | ||
558 | ||
559 | ||
560 | ||
561 | ||
562 | ||
563 | ||
564 | ||
565 | ||
566 | ||
567 | ||
568 | ||
569 | [Page 8] Postel | |
570 | \f | |
571 | ||
572 | ||
573 | RFC 821 August 1982 | |
574 | Simple Mail Transfer Protocol | |
575 | ||
576 | ||
577 | ||
578 | ------------------------------------------------------------- | |
579 | ||
580 | Example of Verifying a User Name | |
581 | ||
582 | Either | |
583 | ||
584 | S: VRFY Smith | |
585 | R: 250 Fred Smith <Smith@USC-ISIF.ARPA> | |
586 | ||
587 | Or | |
588 | ||
589 | S: VRFY Smith | |
590 | R: 251 User not local; will forward to <Smith@USC-ISIQ.ARPA> | |
591 | ||
592 | Or | |
593 | ||
594 | S: VRFY Jones | |
595 | R: 550 String does not match anything. | |
596 | ||
597 | Or | |
598 | ||
599 | S: VRFY Jones | |
600 | R: 551 User not local; please try <Jones@USC-ISIQ.ARPA> | |
601 | ||
602 | Or | |
603 | ||
604 | S: VRFY Gourzenkyinplatz | |
605 | R: 553 User ambiguous. | |
606 | ||
607 | Example 3 | |
608 | ||
609 | ------------------------------------------------------------- | |
610 | ||
611 | ||
612 | ||
613 | ||
614 | ||
615 | ||
616 | ||
617 | ||
618 | ||
619 | ||
620 | ||
621 | ||
622 | ||
623 | ||
624 | ||
625 | ||
626 | ||
627 | Postel [Page 9] | |
628 | \f | |
629 | ||
630 | ||
631 | August 1982 RFC 821 | |
632 | Simple Mail Transfer Protocol | |
633 | ||
634 | ||
635 | ||
636 | The case of expanding a mailbox list requires a multiline reply as | |
637 | shown in example 4. | |
638 | ||
639 | ------------------------------------------------------------- | |
640 | ||
641 | Example of Expanding a Mailing List | |
642 | ||
643 | Either | |
644 | ||
645 | S: EXPN Example-People | |
646 | R: 250-Jon Postel <Postel@USC-ISIF.ARPA> | |
647 | R: 250-Fred Fonebone <Fonebone@USC-ISIQ.ARPA> | |
648 | R: 250-Sam Q. Smith <SQSmith@USC-ISIQ.ARPA> | |
649 | R: 250-Quincy Smith <@USC-ISIF.ARPA:Q-Smith@ISI-VAXA.ARPA> | |
650 | R: 250-<joe@foo-unix.ARPA> | |
651 | R: 250 <xyz@bar-unix.ARPA> | |
652 | ||
653 | Or | |
654 | ||
655 | S: EXPN Executive-Washroom-List | |
656 | R: 550 Access Denied to You. | |
657 | ||
658 | Example 4 | |
659 | ||
660 | ------------------------------------------------------------- | |
661 | ||
662 | The character string arguments of the VRFY and EXPN commands | |
663 | cannot be further restricted due to the variety of implementations | |
664 | of the user name and mailbox list concepts. On some systems it | |
665 | may be appropriate for the argument of the EXPN command to be a | |
666 | file name for a file containing a mailing list, but again there is | |
667 | a variety of file naming conventions in the Internet. | |
668 | ||
669 | The VRFY and EXPN commands are not included in the minimum | |
670 | implementation (Section 4.5.1), and are not required to work | |
671 | across relays when they are implemented. | |
672 | ||
673 | ||
674 | ||
675 | ||
676 | ||
677 | ||
678 | ||
679 | ||
680 | ||
681 | ||
682 | ||
683 | ||
684 | ||
685 | [Page 10] Postel | |
686 | \f | |
687 | ||
688 | ||
689 | RFC 821 August 1982 | |
690 | Simple Mail Transfer Protocol | |
691 | ||
692 | ||
693 | ||
694 | 3.4. SENDING AND MAILING | |
695 | ||
696 | The main purpose of SMTP is to deliver messages to user's | |
697 | mailboxes. A very similar service provided by some hosts is to | |
698 | deliver messages to user's terminals (provided the user is active | |
699 | on the host). The delivery to the user's mailbox is called | |
700 | "mailing", the delivery to the user's terminal is called | |
701 | "sending". Because in many hosts the implementation of sending is | |
702 | nearly identical to the implementation of mailing these two | |
703 | functions are combined in SMTP. However the sending commands are | |
704 | not included in the required minimum implementation | |
705 | (Section 4.5.1). Users should have the ability to control the | |
706 | writing of messages on their terminals. Most hosts permit the | |
707 | users to accept or refuse such messages. | |
708 | ||
709 | The following three command are defined to support the sending | |
710 | options. These are used in the mail transaction instead of the | |
711 | MAIL command and inform the receiver-SMTP of the special semantics | |
712 | of this transaction: | |
713 | ||
714 | SEND <SP> FROM:<reverse-path> <CRLF> | |
715 | ||
716 | The SEND command requires that the mail data be delivered to | |
717 | the user's terminal. If the user is not active (or not | |
718 | accepting terminal messages) on the host a 450 reply may | |
719 | returned to a RCPT command. The mail transaction is | |
720 | successful if the message is delivered the terminal. | |
721 | ||
722 | SOML <SP> FROM:<reverse-path> <CRLF> | |
723 | ||
724 | The Send Or MaiL command requires that the mail data be | |
725 | delivered to the user's terminal if the user is active (and | |
726 | accepting terminal messages) on the host. If the user is | |
727 | not active (or not accepting terminal messages) then the | |
728 | mail data is entered into the user's mailbox. The mail | |
729 | transaction is successful if the message is delivered either | |
730 | to the terminal or the mailbox. | |
731 | ||
732 | SAML <SP> FROM:<reverse-path> <CRLF> | |
733 | ||
734 | The Send And MaiL command requires that the mail data be | |
735 | delivered to the user's terminal if the user is active (and | |
736 | accepting terminal messages) on the host. In any case the | |
737 | mail data is entered into the user's mailbox. The mail | |
738 | transaction is successful if the message is delivered the | |
739 | mailbox. | |
740 | ||
741 | ||
742 | ||
743 | Postel [Page 11] | |
744 | \f | |
745 | ||
746 | ||
747 | August 1982 RFC 821 | |
748 | Simple Mail Transfer Protocol | |
749 | ||
750 | ||
751 | ||
752 | The same reply codes that are used for the MAIL commands are used | |
753 | for these commands. | |
754 | ||
755 | ||
756 | ||
757 | ||
758 | ||
759 | ||
760 | ||
761 | ||
762 | ||
763 | ||
764 | ||
765 | ||
766 | ||
767 | ||
768 | ||
769 | ||
770 | ||
771 | ||
772 | ||
773 | ||
774 | ||
775 | ||
776 | ||
777 | ||
778 | ||
779 | ||
780 | ||
781 | ||
782 | ||
783 | ||
784 | ||
785 | ||
786 | ||
787 | ||
788 | ||
789 | ||
790 | ||
791 | ||
792 | ||
793 | ||
794 | ||
795 | ||
796 | ||
797 | ||
798 | ||
799 | ||
800 | ||
801 | [Page 12] Postel | |
802 | \f | |
803 | ||
804 | ||
805 | RFC 821 August 1982 | |
806 | Simple Mail Transfer Protocol | |
807 | ||
808 | ||
809 | ||
810 | 3.5. OPENING AND CLOSING | |
811 | ||
812 | At the time the transmission channel is opened there is an | |
813 | exchange to ensure that the hosts are communicating with the hosts | |
814 | they think they are. | |
815 | ||
816 | The following two commands are used in transmission channel | |
817 | opening and closing: | |
818 | ||
819 | HELO <SP> <domain> <CRLF> | |
820 | ||
821 | QUIT <CRLF> | |
822 | ||
823 | In the HELO command the host sending the command identifies | |
824 | itself; the command may be interpreted as saying "Hello, I am | |
825 | <domain>". | |
826 | ||
827 | ------------------------------------------------------------- | |
828 | ||
829 | Example of Connection Opening | |
830 | ||
831 | R: 220 BBN-UNIX.ARPA Simple Mail Transfer Service Ready | |
832 | S: HELO USC-ISIF.ARPA | |
833 | R: 250 BBN-UNIX.ARPA | |
834 | ||
835 | Example 5 | |
836 | ||
837 | ------------------------------------------------------------- | |
838 | ||
839 | ------------------------------------------------------------- | |
840 | ||
841 | Example of Connection Closing | |
842 | ||
843 | S: QUIT | |
844 | R: 221 BBN-UNIX.ARPA Service closing transmission channel | |
845 | ||
846 | Example 6 | |
847 | ||
848 | ------------------------------------------------------------- | |
849 | ||
850 | ||
851 | ||
852 | ||
853 | ||
854 | ||
855 | ||
856 | ||
857 | ||
858 | ||
859 | Postel [Page 13] | |
860 | \f | |
861 | ||
862 | ||
863 | August 1982 RFC 821 | |
864 | Simple Mail Transfer Protocol | |
865 | ||
866 | ||
867 | ||
868 | 3.6. RELAYING | |
869 | ||
870 | The forward-path may be a source route of the form | |
871 | "@ONE,@TWO:JOE@THREE", where ONE, TWO, and THREE are hosts. This | |
872 | form is used to emphasize the distinction between an address and a | |
873 | route. The mailbox is an absolute address, and the route is | |
874 | information about how to get there. The two concepts should not | |
875 | be confused. | |
876 | ||
877 | Conceptually the elements of the forward-path are moved to the | |
878 | reverse-path as the message is relayed from one server-SMTP to | |
879 | another. The reverse-path is a reverse source route, (i.e., a | |
880 | source route from the current location of the message to the | |
881 | originator of the message). When a server-SMTP deletes its | |
882 | identifier from the forward-path and inserts it into the | |
883 | reverse-path, it must use the name it is known by in the | |
884 | environment it is sending into, not the environment the mail came | |
885 | from, in case the server-SMTP is known by different names in | |
886 | different environments. | |
887 | ||
888 | If when the message arrives at an SMTP the first element of the | |
889 | forward-path is not the identifier of that SMTP the element is not | |
890 | deleted from the forward-path and is used to determine the next | |
891 | SMTP to send the message to. In any case, the SMTP adds its own | |
892 | identifier to the reverse-path. | |
893 | ||
894 | Using source routing the receiver-SMTP receives mail to be relayed | |
895 | to another server-SMTP The receiver-SMTP may accept or reject the | |
896 | task of relaying the mail in the same way it accepts or rejects | |
897 | mail for a local user. The receiver-SMTP transforms the command | |
898 | arguments by moving its own identifier from the forward-path to | |
899 | the beginning of the reverse-path. The receiver-SMTP then becomes | |
900 | a sender-SMTP, establishes a transmission channel to the next SMTP | |
901 | in the forward-path, and sends it the mail. | |
902 | ||
903 | The first host in the reverse-path should be the host sending the | |
904 | SMTP commands, and the first host in the forward-path should be | |
905 | the host receiving the SMTP commands. | |
906 | ||
907 | Notice that the forward-path and reverse-path appear in the SMTP | |
908 | commands and replies, but not necessarily in the message. That | |
909 | is, there is no need for these paths and especially this syntax to | |
910 | appear in the "To:" , "From:", "CC:", etc. fields of the message | |
911 | header. | |
912 | ||
913 | If a server-SMTP has accepted the task of relaying the mail and | |
914 | ||
915 | ||
916 | ||
917 | [Page 14] Postel | |
918 | \f | |
919 | ||
920 | ||
921 | RFC 821 August 1982 | |
922 | Simple Mail Transfer Protocol | |
923 | ||
924 | ||
925 | ||
926 | later finds that the forward-path is incorrect or that the mail | |
927 | cannot be delivered for whatever reason, then it must construct an | |
928 | "undeliverable mail" notification message and send it to the | |
929 | originator of the undeliverable mail (as indicated by the | |
930 | reverse-path). | |
931 | ||
932 | This notification message must be from the server-SMTP at this | |
933 | host. Of course, server-SMTPs should not send notification | |
934 | messages about problems with notification messages. One way to | |
935 | prevent loops in error reporting is to specify a null reverse-path | |
936 | in the MAIL command of a notification message. When such a | |
937 | message is relayed it is permissible to leave the reverse-path | |
938 | null. A MAIL command with a null reverse-path appears as follows: | |
939 | ||
940 | MAIL FROM:<> | |
941 | ||
942 | An undeliverable mail notification message is shown in example 7. | |
943 | This notification is in response to a message originated by JOE at | |
944 | HOSTW and sent via HOSTX to HOSTY with instructions to relay it on | |
945 | to HOSTZ. What we see in the example is the transaction between | |
946 | HOSTY and HOSTX, which is the first step in the return of the | |
947 | notification message. | |
948 | ||
949 | ||
950 | ||
951 | ||
952 | ||
953 | ||
954 | ||
955 | ||
956 | ||
957 | ||
958 | ||
959 | ||
960 | ||
961 | ||
962 | ||
963 | ||
964 | ||
965 | ||
966 | ||
967 | ||
968 | ||
969 | ||
970 | ||
971 | ||
972 | ||
973 | ||
974 | ||
975 | Postel [Page 15] | |
976 | \f | |
977 | ||
978 | ||
979 | August 1982 RFC 821 | |
980 | Simple Mail Transfer Protocol | |
981 | ||
982 | ||
983 | ||
984 | ------------------------------------------------------------- | |
985 | ||
986 | Example Undeliverable Mail Notification Message | |
987 | ||
988 | S: MAIL FROM:<> | |
989 | R: 250 ok | |
990 | S: RCPT TO:<@HOSTX.ARPA:JOE@HOSTW.ARPA> | |
991 | R: 250 ok | |
992 | S: DATA | |
993 | R: 354 send the mail data, end with . | |
994 | S: Date: 23 Oct 81 11:22:33 | |
995 | S: From: SMTP@HOSTY.ARPA | |
996 | S: To: JOE@HOSTW.ARPA | |
997 | S: Subject: Mail System Problem | |
998 | S: | |
999 | S: Sorry JOE, your message to SAM@HOSTZ.ARPA lost. | |
1000 | S: HOSTZ.ARPA said this: | |
1001 | S: "550 No Such User" | |
1002 | S: . | |
1003 | R: 250 ok | |
1004 | ||
1005 | Example 7 | |
1006 | ||
1007 | ------------------------------------------------------------- | |
1008 | ||
1009 | ||
1010 | ||
1011 | ||
1012 | ||
1013 | ||
1014 | ||
1015 | ||
1016 | ||
1017 | ||
1018 | ||
1019 | ||
1020 | ||
1021 | ||
1022 | ||
1023 | ||
1024 | ||
1025 | ||
1026 | ||
1027 | ||
1028 | ||
1029 | ||
1030 | ||
1031 | ||
1032 | ||
1033 | [Page 16] Postel | |
1034 | \f | |
1035 | ||
1036 | ||
1037 | RFC 821 August 1982 | |
1038 | Simple Mail Transfer Protocol | |
1039 | ||
1040 | ||
1041 | ||
1042 | 3.7. DOMAINS | |
1043 | ||
1044 | Domains are a recently introduced concept in the ARPA Internet | |
1045 | mail system. The use of domains changes the address space from a | |
1046 | flat global space of simple character string host names to a | |
1047 | hierarchically structured rooted tree of global addresses. The | |
1048 | host name is replaced by a domain and host designator which is a | |
1049 | sequence of domain element strings separated by periods with the | |
1050 | understanding that the domain elements are ordered from the most | |
1051 | specific to the most general. | |
1052 | ||
1053 | For example, "USC-ISIF.ARPA", "Fred.Cambridge.UK", and | |
1054 | "PC7.LCS.MIT.ARPA" might be host-and-domain identifiers. | |
1055 | ||
1056 | Whenever domain names are used in SMTP only the official names are | |
1057 | used, the use of nicknames or aliases is not allowed. | |
1058 | ||
1059 | ||
1060 | ||
1061 | ||
1062 | ||
1063 | ||
1064 | ||
1065 | ||
1066 | ||
1067 | ||
1068 | ||
1069 | ||
1070 | ||
1071 | ||
1072 | ||
1073 | ||
1074 | ||
1075 | ||
1076 | ||
1077 | ||
1078 | ||
1079 | ||
1080 | ||
1081 | ||
1082 | ||
1083 | ||
1084 | ||
1085 | ||
1086 | ||
1087 | ||
1088 | ||
1089 | ||
1090 | ||
1091 | Postel [Page 17] | |
1092 | \f | |
1093 | ||
1094 | ||
1095 | August 1982 RFC 821 | |
1096 | Simple Mail Transfer Protocol | |
1097 | ||
1098 | ||
1099 | ||
1100 | 3.8. CHANGING ROLES | |
1101 | ||
1102 | The TURN command may be used to reverse the roles of the two | |
1103 | programs communicating over the transmission channel. | |
1104 | ||
1105 | If program-A is currently the sender-SMTP and it sends the TURN | |
1106 | command and receives an ok reply (250) then program-A becomes the | |
1107 | receiver-SMTP. | |
1108 | ||
1109 | If program-B is currently the receiver-SMTP and it receives the | |
1110 | TURN command and sends an ok reply (250) then program-B becomes | |
1111 | the sender-SMTP. | |
1112 | ||
1113 | To refuse to change roles the receiver sends the 502 reply. | |
1114 | ||
1115 | Please note that this command is optional. It would not normally | |
1116 | be used in situations where the transmission channel is TCP. | |
1117 | However, when the cost of establishing the transmission channel is | |
1118 | high, this command may be quite useful. For example, this command | |
1119 | may be useful in supporting be mail exchange using the public | |
1120 | switched telephone system as a transmission channel, especially if | |
1121 | some hosts poll other hosts for mail exchanges. | |
1122 | ||
1123 | ||
1124 | ||
1125 | ||
1126 | ||
1127 | ||
1128 | ||
1129 | ||
1130 | ||
1131 | ||
1132 | ||
1133 | ||
1134 | ||
1135 | ||
1136 | ||
1137 | ||
1138 | ||
1139 | ||
1140 | ||
1141 | ||
1142 | ||
1143 | ||
1144 | ||
1145 | ||
1146 | ||
1147 | ||
1148 | ||
1149 | [Page 18] Postel | |
1150 | \f | |
1151 | ||
1152 | ||
1153 | RFC 821 August 1982 | |
1154 | Simple Mail Transfer Protocol | |
1155 | ||
1156 | ||
1157 | ||
1158 | 4. THE SMTP SPECIFICATIONS | |
1159 | ||
1160 | 4.1. SMTP COMMANDS | |
1161 | ||
1162 | 4.1.1. COMMAND SEMANTICS | |
1163 | ||
1164 | The SMTP commands define the mail transfer or the mail system | |
1165 | function requested by the user. SMTP commands are character | |
1166 | strings terminated by <CRLF>. The command codes themselves are | |
1167 | alphabetic characters terminated by <SP> if parameters follow | |
1168 | and <CRLF> otherwise. The syntax of mailboxes must conform to | |
1169 | receiver site conventions. The SMTP commands are discussed | |
1170 | below. The SMTP replies are discussed in the Section 4.2. | |
1171 | ||
1172 | A mail transaction involves several data objects which are | |
1173 | communicated as arguments to different commands. The | |
1174 | reverse-path is the argument of the MAIL command, the | |
1175 | forward-path is the argument of the RCPT command, and the mail | |
1176 | data is the argument of the DATA command. These arguments or | |
1177 | data objects must be transmitted and held pending the | |
1178 | confirmation communicated by the end of mail data indication | |
1179 | which finalizes the transaction. The model for this is that | |
1180 | distinct buffers are provided to hold the types of data | |
1181 | objects, that is, there is a reverse-path buffer, a | |
1182 | forward-path buffer, and a mail data buffer. Specific commands | |
1183 | cause information to be appended to a specific buffer, or cause | |
1184 | one or more buffers to be cleared. | |
1185 | ||
1186 | HELLO (HELO) | |
1187 | ||
1188 | This command is used to identify the sender-SMTP to the | |
1189 | receiver-SMTP. The argument field contains the host name of | |
1190 | the sender-SMTP. | |
1191 | ||
1192 | The receiver-SMTP identifies itself to the sender-SMTP in | |
1193 | the connection greeting reply, and in the response to this | |
1194 | command. | |
1195 | ||
1196 | This command and an OK reply to it confirm that both the | |
1197 | sender-SMTP and the receiver-SMTP are in the initial state, | |
1198 | that is, there is no transaction in progress and all state | |
1199 | tables and buffers are cleared. | |
1200 | ||
1201 | ||
1202 | ||
1203 | ||
1204 | ||
1205 | ||
1206 | ||
1207 | Postel [Page 19] | |
1208 | \f | |
1209 | ||
1210 | ||
1211 | August 1982 RFC 821 | |
1212 | Simple Mail Transfer Protocol | |
1213 | ||
1214 | ||
1215 | ||
1216 | MAIL (MAIL) | |
1217 | ||
1218 | This command is used to initiate a mail transaction in which | |
1219 | the mail data is delivered to one or more mailboxes. The | |
1220 | argument field contains a reverse-path. | |
1221 | ||
1222 | The reverse-path consists of an optional list of hosts and | |
1223 | the sender mailbox. When the list of hosts is present, it | |
1224 | is a "reverse" source route and indicates that the mail was | |
1225 | relayed through each host on the list (the first host in the | |
1226 | list was the most recent relay). This list is used as a | |
1227 | source route to return non-delivery notices to the sender. | |
1228 | As each relay host adds itself to the beginning of the list, | |
1229 | it must use its name as known in the IPCE to which it is | |
1230 | relaying the mail rather than the IPCE from which the mail | |
1231 | came (if they are different). In some types of error | |
1232 | reporting messages (for example, undeliverable mail | |
1233 | notifications) the reverse-path may be null (see Example 7). | |
1234 | ||
1235 | This command clears the reverse-path buffer, the | |
1236 | forward-path buffer, and the mail data buffer; and inserts | |
1237 | the reverse-path information from this command into the | |
1238 | reverse-path buffer. | |
1239 | ||
1240 | RECIPIENT (RCPT) | |
1241 | ||
1242 | This command is used to identify an individual recipient of | |
1243 | the mail data; multiple recipients are specified by multiple | |
1244 | use of this command. | |
1245 | ||
1246 | The forward-path consists of an optional list of hosts and a | |
1247 | required destination mailbox. When the list of hosts is | |
1248 | present, it is a source route and indicates that the mail | |
1249 | must be relayed to the next host on the list. If the | |
1250 | receiver-SMTP does not implement the relay function it may | |
1251 | user the same reply it would for an unknown local user | |
1252 | (550). | |
1253 | ||
1254 | When mail is relayed, the relay host must remove itself from | |
1255 | the beginning forward-path and put itself at the beginning | |
1256 | of the reverse-path. When mail reaches its ultimate | |
1257 | destination (the forward-path contains only a destination | |
1258 | mailbox), the receiver-SMTP inserts it into the destination | |
1259 | mailbox in accordance with its host mail conventions. | |
1260 | ||
1261 | ||
1262 | ||
1263 | ||
1264 | ||
1265 | [Page 20] Postel | |
1266 | \f | |
1267 | ||
1268 | ||
1269 | RFC 821 August 1982 | |
1270 | Simple Mail Transfer Protocol | |
1271 | ||
1272 | ||
1273 | ||
1274 | For example, mail received at relay host A with arguments | |
1275 | ||
1276 | FROM:<USERX@HOSTY.ARPA> | |
1277 | TO:<@HOSTA.ARPA,@HOSTB.ARPA:USERC@HOSTD.ARPA> | |
1278 | ||
1279 | will be relayed on to host B with arguments | |
1280 | ||
1281 | FROM:<@HOSTA.ARPA:USERX@HOSTY.ARPA> | |
1282 | TO:<@HOSTB.ARPA:USERC@HOSTD.ARPA>. | |
1283 | ||
1284 | This command causes its forward-path argument to be appended | |
1285 | to the forward-path buffer. | |
1286 | ||
1287 | DATA (DATA) | |
1288 | ||
1289 | The receiver treats the lines following the command as mail | |
1290 | data from the sender. This command causes the mail data | |
1291 | from this command to be appended to the mail data buffer. | |
1292 | The mail data may contain any of the 128 ASCII character | |
1293 | codes. | |
1294 | ||
1295 | The mail data is terminated by a line containing only a | |
1296 | period, that is the character sequence "<CRLF>.<CRLF>" (see | |
1297 | Section 4.5.2 on Transparency). This is the end of mail | |
1298 | data indication. | |
1299 | ||
1300 | The end of mail data indication requires that the receiver | |
1301 | must now process the stored mail transaction information. | |
1302 | This processing consumes the information in the reverse-path | |
1303 | buffer, the forward-path buffer, and the mail data buffer, | |
1304 | and on the completion of this command these buffers are | |
1305 | cleared. If the processing is successful the receiver must | |
1306 | send an OK reply. If the processing fails completely the | |
1307 | receiver must send a failure reply. | |
1308 | ||
1309 | When the receiver-SMTP accepts a message either for relaying | |
1310 | or for final delivery it inserts at the beginning of the | |
1311 | mail data a time stamp line. The time stamp line indicates | |
1312 | the identity of the host that sent the message, and the | |
1313 | identity of the host that received the message (and is | |
1314 | inserting this time stamp), and the date and time the | |
1315 | message was received. Relayed messages will have multiple | |
1316 | time stamp lines. | |
1317 | ||
1318 | When the receiver-SMTP makes the "final delivery" of a | |
1319 | message it inserts at the beginning of the mail data a | |
1320 | ||
1321 | ||
1322 | ||
1323 | Postel [Page 21] | |
1324 | \f | |
1325 | ||
1326 | ||
1327 | August 1982 RFC 821 | |
1328 | Simple Mail Transfer Protocol | |
1329 | ||
1330 | ||
1331 | ||
1332 | return path line. The return path line preserves the | |
1333 | information in the <reverse-path> from the MAIL command. | |
1334 | Here, final delivery means the message leaves the SMTP | |
1335 | world. Normally, this would mean it has been delivered to | |
1336 | the destination user, but in some cases it may be further | |
1337 | processed and transmitted by another mail system. | |
1338 | ||
1339 | It is possible for the mailbox in the return path be | |
1340 | different from the actual sender's mailbox, for example, | |
1341 | if error responses are to be delivered a special error | |
1342 | handling mailbox rather than the message senders. | |
1343 | ||
1344 | The preceding two paragraphs imply that the final mail data | |
1345 | will begin with a return path line, followed by one or more | |
1346 | time stamp lines. These lines will be followed by the mail | |
1347 | data header and body [2]. See Example 8. | |
1348 | ||
1349 | Special mention is needed of the response and further action | |
1350 | required when the processing following the end of mail data | |
1351 | indication is partially successful. This could arise if | |
1352 | after accepting several recipients and the mail data, the | |
1353 | receiver-SMTP finds that the mail data can be successfully | |
1354 | delivered to some of the recipients, but it cannot be to | |
1355 | others (for example, due to mailbox space allocation | |
1356 | problems). In such a situation, the response to the DATA | |
1357 | command must be an OK reply. But, the receiver-SMTP must | |
1358 | compose and send an "undeliverable mail" notification | |
1359 | message to the originator of the message. Either a single | |
1360 | notification which lists all of the recipients that failed | |
1361 | to get the message, or separate notification messages must | |
1362 | be sent for each failed recipient (see Example 7). All | |
1363 | undeliverable mail notification messages are sent using the | |
1364 | MAIL command (even if they result from processing a SEND, | |
1365 | SOML, or SAML command). | |
1366 | ||
1367 | ||
1368 | ||
1369 | ||
1370 | ||
1371 | ||
1372 | ||
1373 | ||
1374 | ||
1375 | ||
1376 | ||
1377 | ||
1378 | ||
1379 | ||
1380 | ||
1381 | [Page 22] Postel | |
1382 | \f | |
1383 | ||
1384 | ||
1385 | RFC 821 August 1982 | |
1386 | Simple Mail Transfer Protocol | |
1387 | ||
1388 | ||
1389 | ||
1390 | ------------------------------------------------------------- | |
1391 | ||
1392 | Example of Return Path and Received Time Stamps | |
1393 | ||
1394 | Return-Path: <@GHI.ARPA,@DEF.ARPA,@ABC.ARPA:JOE@ABC.ARPA> | |
1395 | Received: from GHI.ARPA by JKL.ARPA ; 27 Oct 81 15:27:39 PST | |
1396 | Received: from DEF.ARPA by GHI.ARPA ; 27 Oct 81 15:15:13 PST | |
1397 | Received: from ABC.ARPA by DEF.ARPA ; 27 Oct 81 15:01:59 PST | |
1398 | Date: 27 Oct 81 15:01:01 PST | |
1399 | From: JOE@ABC.ARPA | |
1400 | Subject: Improved Mailing System Installed | |
1401 | To: SAM@JKL.ARPA | |
1402 | ||
1403 | This is to inform you that ... | |
1404 | ||
1405 | Example 8 | |
1406 | ||
1407 | ------------------------------------------------------------- | |
1408 | ||
1409 | SEND (SEND) | |
1410 | ||
1411 | This command is used to initiate a mail transaction in which | |
1412 | the mail data is delivered to one or more terminals. The | |
1413 | argument field contains a reverse-path. This command is | |
1414 | successful if the message is delivered to a terminal. | |
1415 | ||
1416 | The reverse-path consists of an optional list of hosts and | |
1417 | the sender mailbox. When the list of hosts is present, it | |
1418 | is a "reverse" source route and indicates that the mail was | |
1419 | relayed through each host on the list (the first host in the | |
1420 | list was the most recent relay). This list is used as a | |
1421 | source route to return non-delivery notices to the sender. | |
1422 | As each relay host adds itself to the beginning of the list, | |
1423 | it must use its name as known in the IPCE to which it is | |
1424 | relaying the mail rather than the IPCE from which the mail | |
1425 | came (if they are different). | |
1426 | ||
1427 | This command clears the reverse-path buffer, the | |
1428 | forward-path buffer, and the mail data buffer; and inserts | |
1429 | the reverse-path information from this command into the | |
1430 | reverse-path buffer. | |
1431 | ||
1432 | SEND OR MAIL (SOML) | |
1433 | ||
1434 | This command is used to initiate a mail transaction in which | |
1435 | the mail data is delivered to one or more terminals or | |
1436 | ||
1437 | ||
1438 | ||
1439 | Postel [Page 23] | |
1440 | \f | |
1441 | ||
1442 | ||
1443 | August 1982 RFC 821 | |
1444 | Simple Mail Transfer Protocol | |
1445 | ||
1446 | ||
1447 | ||
1448 | mailboxes. For each recipient the mail data is delivered to | |
1449 | the recipient's terminal if the recipient is active on the | |
1450 | host (and accepting terminal messages), otherwise to the | |
1451 | recipient's mailbox. The argument field contains a | |
1452 | reverse-path. This command is successful if the message is | |
1453 | delivered to a terminal or the mailbox. | |
1454 | ||
1455 | The reverse-path consists of an optional list of hosts and | |
1456 | the sender mailbox. When the list of hosts is present, it | |
1457 | is a "reverse" source route and indicates that the mail was | |
1458 | relayed through each host on the list (the first host in the | |
1459 | list was the most recent relay). This list is used as a | |
1460 | source route to return non-delivery notices to the sender. | |
1461 | As each relay host adds itself to the beginning of the list, | |
1462 | it must use its name as known in the IPCE to which it is | |
1463 | relaying the mail rather than the IPCE from which the mail | |
1464 | came (if they are different). | |
1465 | ||
1466 | This command clears the reverse-path buffer, the | |
1467 | forward-path buffer, and the mail data buffer; and inserts | |
1468 | the reverse-path information from this command into the | |
1469 | reverse-path buffer. | |
1470 | ||
1471 | SEND AND MAIL (SAML) | |
1472 | ||
1473 | This command is used to initiate a mail transaction in which | |
1474 | the mail data is delivered to one or more terminals and | |
1475 | mailboxes. For each recipient the mail data is delivered to | |
1476 | the recipient's terminal if the recipient is active on the | |
1477 | host (and accepting terminal messages), and for all | |
1478 | recipients to the recipient's mailbox. The argument field | |
1479 | contains a reverse-path. This command is successful if the | |
1480 | message is delivered to the mailbox. | |
1481 | ||
1482 | The reverse-path consists of an optional list of hosts and | |
1483 | the sender mailbox. When the list of hosts is present, it | |
1484 | is a "reverse" source route and indicates that the mail was | |
1485 | relayed through each host on the list (the first host in the | |
1486 | list was the most recent relay). This list is used as a | |
1487 | source route to return non-delivery notices to the sender. | |
1488 | As each relay host adds itself to the beginning of the list, | |
1489 | it must use its name as known in the IPCE to which it is | |
1490 | relaying the mail rather than the IPCE from which the mail | |
1491 | came (if they are different). | |
1492 | ||
1493 | This command clears the reverse-path buffer, the | |
1494 | ||
1495 | ||
1496 | ||
1497 | [Page 24] Postel | |
1498 | \f | |
1499 | ||
1500 | ||
1501 | RFC 821 August 1982 | |
1502 | Simple Mail Transfer Protocol | |
1503 | ||
1504 | ||
1505 | ||
1506 | forward-path buffer, and the mail data buffer; and inserts | |
1507 | the reverse-path information from this command into the | |
1508 | reverse-path buffer. | |
1509 | ||
1510 | RESET (RSET) | |
1511 | ||
1512 | This command specifies that the current mail transaction is | |
1513 | to be aborted. Any stored sender, recipients, and mail data | |
1514 | must be discarded, and all buffers and state tables cleared. | |
1515 | The receiver must send an OK reply. | |
1516 | ||
1517 | VERIFY (VRFY) | |
1518 | ||
1519 | This command asks the receiver to confirm that the argument | |
1520 | identifies a user. If it is a user name, the full name of | |
1521 | the user (if known) and the fully specified mailbox are | |
1522 | returned. | |
1523 | ||
1524 | This command has no effect on any of the reverse-path | |
1525 | buffer, the forward-path buffer, or the mail data buffer. | |
1526 | ||
1527 | EXPAND (EXPN) | |
1528 | ||
1529 | This command asks the receiver to confirm that the argument | |
1530 | identifies a mailing list, and if so, to return the | |
1531 | membership of that list. The full name of the users (if | |
1532 | known) and the fully specified mailboxes are returned in a | |
1533 | multiline reply. | |
1534 | ||
1535 | This command has no effect on any of the reverse-path | |
1536 | buffer, the forward-path buffer, or the mail data buffer. | |
1537 | ||
1538 | HELP (HELP) | |
1539 | ||
1540 | This command causes the receiver to send helpful information | |
1541 | to the sender of the HELP command. The command may take an | |
1542 | argument (e.g., any command name) and return more specific | |
1543 | information as a response. | |
1544 | ||
1545 | This command has no effect on any of the reverse-path | |
1546 | buffer, the forward-path buffer, or the mail data buffer. | |
1547 | ||
1548 | ||
1549 | ||
1550 | ||
1551 | ||
1552 | ||
1553 | ||
1554 | ||
1555 | Postel [Page 25] | |
1556 | \f | |
1557 | ||
1558 | ||
1559 | August 1982 RFC 821 | |
1560 | Simple Mail Transfer Protocol | |
1561 | ||
1562 | ||
1563 | ||
1564 | NOOP (NOOP) | |
1565 | ||
1566 | This command does not affect any parameters or previously | |
1567 | entered commands. It specifies no action other than that | |
1568 | the receiver send an OK reply. | |
1569 | ||
1570 | This command has no effect on any of the reverse-path | |
1571 | buffer, the forward-path buffer, or the mail data buffer. | |
1572 | ||
1573 | QUIT (QUIT) | |
1574 | ||
1575 | This command specifies that the receiver must send an OK | |
1576 | reply, and then close the transmission channel. | |
1577 | ||
1578 | The receiver should not close the transmission channel until | |
1579 | it receives and replies to a QUIT command (even if there was | |
1580 | an error). The sender should not close the transmission | |
1581 | channel until it send a QUIT command and receives the reply | |
1582 | (even if there was an error response to a previous command). | |
1583 | If the connection is closed prematurely the receiver should | |
1584 | act as if a RSET command had been received (canceling any | |
1585 | pending transaction, but not undoing any previously | |
1586 | completed transaction), the sender should act as if the | |
1587 | command or transaction in progress had received a temporary | |
1588 | error (4xx). | |
1589 | ||
1590 | TURN (TURN) | |
1591 | ||
1592 | This command specifies that the receiver must either (1) | |
1593 | send an OK reply and then take on the role of the | |
1594 | sender-SMTP, or (2) send a refusal reply and retain the role | |
1595 | of the receiver-SMTP. | |
1596 | ||
1597 | If program-A is currently the sender-SMTP and it sends the | |
1598 | TURN command and receives an OK reply (250) then program-A | |
1599 | becomes the receiver-SMTP. Program-A is then in the initial | |
1600 | state as if the transmission channel just opened, and it | |
1601 | then sends the 220 service ready greeting. | |
1602 | ||
1603 | If program-B is currently the receiver-SMTP and it receives | |
1604 | the TURN command and sends an OK reply (250) then program-B | |
1605 | becomes the sender-SMTP. Program-B is then in the initial | |
1606 | state as if the transmission channel just opened, and it | |
1607 | then expects to receive the 220 service ready greeting. | |
1608 | ||
1609 | To refuse to change roles the receiver sends the 502 reply. | |
1610 | ||
1611 | ||
1612 | ||
1613 | [Page 26] Postel | |
1614 | \f | |
1615 | ||
1616 | ||
1617 | RFC 821 August 1982 | |
1618 | Simple Mail Transfer Protocol | |
1619 | ||
1620 | ||
1621 | ||
1622 | There are restrictions on the order in which these command may | |
1623 | be used. | |
1624 | ||
1625 | The first command in a session must be the HELO command. | |
1626 | The HELO command may be used later in a session as well. If | |
1627 | the HELO command argument is not acceptable a 501 failure | |
1628 | reply must be returned and the receiver-SMTP must stay in | |
1629 | the same state. | |
1630 | ||
1631 | The NOOP, HELP, EXPN, and VRFY commands can be used at any | |
1632 | time during a session. | |
1633 | ||
1634 | The MAIL, SEND, SOML, or SAML commands begin a mail | |
1635 | transaction. Once started a mail transaction consists of | |
1636 | one of the transaction beginning commands, one or more RCPT | |
1637 | commands, and a DATA command, in that order. A mail | |
1638 | transaction may be aborted by the RSET command. There may | |
1639 | be zero or more transactions in a session. | |
1640 | ||
1641 | If the transaction beginning command argument is not | |
1642 | acceptable a 501 failure reply must be returned and the | |
1643 | receiver-SMTP must stay in the same state. If the commands | |
1644 | in a transaction are out of order a 503 failure reply must | |
1645 | be returned and the receiver-SMTP must stay in the same | |
1646 | state. | |
1647 | ||
1648 | The last command in a session must be the QUIT command. The | |
1649 | QUIT command can not be used at any other time in a session. | |
1650 | ||
1651 | 4.1.2. COMMAND SYNTAX | |
1652 | ||
1653 | The commands consist of a command code followed by an argument | |
1654 | field. Command codes are four alphabetic characters. Upper | |
1655 | and lower case alphabetic characters are to be treated | |
1656 | identically. Thus, any of the following may represent the mail | |
1657 | command: | |
1658 | ||
1659 | MAIL Mail mail MaIl mAIl | |
1660 | ||
1661 | This also applies to any symbols representing parameter values, | |
1662 | such as "TO" or "to" for the forward-path. Command codes and | |
1663 | the argument fields are separated by one or more spaces. | |
1664 | However, within the reverse-path and forward-path arguments | |
1665 | case is important. In particular, in some hosts the user | |
1666 | "smith" is different from the user "Smith". | |
1667 | ||
1668 | ||
1669 | ||
1670 | ||
1671 | Postel [Page 27] | |
1672 | \f | |
1673 | ||
1674 | ||
1675 | August 1982 RFC 821 | |
1676 | Simple Mail Transfer Protocol | |
1677 | ||
1678 | ||
1679 | ||
1680 | The argument field consists of a variable length character | |
1681 | string ending with the character sequence <CRLF>. The receiver | |
1682 | is to take no action until this sequence is received. | |
1683 | ||
1684 | Square brackets denote an optional argument field. If the | |
1685 | option is not taken, the appropriate default is implied. | |
1686 | ||
1687 | ||
1688 | ||
1689 | ||
1690 | ||
1691 | ||
1692 | ||
1693 | ||
1694 | ||
1695 | ||
1696 | ||
1697 | ||
1698 | ||
1699 | ||
1700 | ||
1701 | ||
1702 | ||
1703 | ||
1704 | ||
1705 | ||
1706 | ||
1707 | ||
1708 | ||
1709 | ||
1710 | ||
1711 | ||
1712 | ||
1713 | ||
1714 | ||
1715 | ||
1716 | ||
1717 | ||
1718 | ||
1719 | ||
1720 | ||
1721 | ||
1722 | ||
1723 | ||
1724 | ||
1725 | ||
1726 | ||
1727 | ||
1728 | ||
1729 | [Page 28] Postel | |
1730 | \f | |
1731 | ||
1732 | ||
1733 | RFC 821 August 1982 | |
1734 | Simple Mail Transfer Protocol | |
1735 | ||
1736 | ||
1737 | ||
1738 | The following are the SMTP commands: | |
1739 | ||
1740 | HELO <SP> <domain> <CRLF> | |
1741 | ||
1742 | MAIL <SP> FROM:<reverse-path> <CRLF> | |
1743 | ||
1744 | RCPT <SP> TO:<forward-path> <CRLF> | |
1745 | ||
1746 | DATA <CRLF> | |
1747 | ||
1748 | RSET <CRLF> | |
1749 | ||
1750 | SEND <SP> FROM:<reverse-path> <CRLF> | |
1751 | ||
1752 | SOML <SP> FROM:<reverse-path> <CRLF> | |
1753 | ||
1754 | SAML <SP> FROM:<reverse-path> <CRLF> | |
1755 | ||
1756 | VRFY <SP> <string> <CRLF> | |
1757 | ||
1758 | EXPN <SP> <string> <CRLF> | |
1759 | ||
1760 | HELP [<SP> <string>] <CRLF> | |
1761 | ||
1762 | NOOP <CRLF> | |
1763 | ||
1764 | QUIT <CRLF> | |
1765 | ||
1766 | TURN <CRLF> | |
1767 | ||
1768 | ||
1769 | ||
1770 | ||
1771 | ||
1772 | ||
1773 | ||
1774 | ||
1775 | ||
1776 | ||
1777 | ||
1778 | ||
1779 | ||
1780 | ||
1781 | ||
1782 | ||
1783 | ||
1784 | ||
1785 | ||
1786 | ||
1787 | Postel [Page 29] | |
1788 | \f | |
1789 | ||
1790 | ||
1791 | August 1982 RFC 821 | |
1792 | Simple Mail Transfer Protocol | |
1793 | ||
1794 | ||
1795 | ||
1796 | The syntax of the above argument fields (using BNF notation | |
1797 | where applicable) is given below. The "..." notation indicates | |
1798 | that a field may be repeated one or more times. | |
1799 | ||
1800 | <reverse-path> ::= <path> | |
1801 | ||
1802 | <forward-path> ::= <path> | |
1803 | ||
1804 | <path> ::= "<" [ <a-d-l> ":" ] <mailbox> ">" | |
1805 | ||
1806 | <a-d-l> ::= <at-domain> | <at-domain> "," <a-d-l> | |
1807 | ||
1808 | <at-domain> ::= "@" <domain> | |
1809 | ||
1810 | <domain> ::= <element> | <element> "." <domain> | |
1811 | ||
1812 | <element> ::= <name> | "#" <number> | "[" <dotnum> "]" | |
1813 | ||
1814 | <mailbox> ::= <local-part> "@" <domain> | |
1815 | ||
1816 | <local-part> ::= <dot-string> | <quoted-string> | |
1817 | ||
1818 | <name> ::= <a> <ldh-str> <let-dig> | |
1819 | ||
1820 | <ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str> | |
1821 | ||
1822 | <let-dig> ::= <a> | <d> | |
1823 | ||
1824 | <let-dig-hyp> ::= <a> | <d> | "-" | |
1825 | ||
1826 | <dot-string> ::= <string> | <string> "." <dot-string> | |
1827 | ||
1828 | <string> ::= <char> | <char> <string> | |
1829 | ||
1830 | <quoted-string> ::= """ <qtext> """ | |
1831 | ||
1832 | <qtext> ::= "\" <x> | "\" <x> <qtext> | <q> | <q> <qtext> | |
1833 | ||
1834 | <char> ::= <c> | "\" <x> | |
1835 | ||
1836 | <dotnum> ::= <snum> "." <snum> "." <snum> "." <snum> | |
1837 | ||
1838 | <number> ::= <d> | <d> <number> | |
1839 | ||
1840 | <CRLF> ::= <CR> <LF> | |
1841 | ||
1842 | ||
1843 | ||
1844 | ||
1845 | [Page 30] Postel | |
1846 | \f | |
1847 | ||
1848 | ||
1849 | RFC 821 August 1982 | |
1850 | Simple Mail Transfer Protocol | |
1851 | ||
1852 | ||
1853 | ||
1854 | <CR> ::= the carriage return character (ASCII code 13) | |
1855 | ||
1856 | <LF> ::= the line feed character (ASCII code 10) | |
1857 | ||
1858 | <SP> ::= the space character (ASCII code 32) | |
1859 | ||
1860 | <snum> ::= one, two, or three digits representing a decimal | |
1861 | integer value in the range 0 through 255 | |
1862 | ||
1863 | <a> ::= any one of the 52 alphabetic characters A through Z | |
1864 | in upper case and a through z in lower case | |
1865 | ||
1866 | <c> ::= any one of the 128 ASCII characters, but not any | |
1867 | <special> or <SP> | |
1868 | ||
1869 | <d> ::= any one of the ten digits 0 through 9 | |
1870 | ||
1871 | <q> ::= any one of the 128 ASCII characters except <CR>, | |
1872 | <LF>, quote ("), or backslash (\) | |
1873 | ||
1874 | <x> ::= any one of the 128 ASCII characters (no exceptions) | |
1875 | ||
1876 | <special> ::= "<" | ">" | "(" | ")" | "[" | "]" | "\" | "." | |
1877 | | "," | ";" | ":" | "@" """ | the control | |
1878 | characters (ASCII codes 0 through 31 inclusive and | |
1879 | 127) | |
1880 | ||
1881 | Note that the backslash, "\", is a quote character, which is | |
1882 | used to indicate that the next character is to be used | |
1883 | literally (instead of its normal interpretation). For example, | |
1884 | "Joe\,Smith" could be used to indicate a single nine character | |
1885 | user field with comma being the fourth character of the field. | |
1886 | ||
1887 | Hosts are generally known by names which are translated to | |
1888 | addresses in each host. Note that the name elements of domains | |
1889 | are the official names -- no use of nicknames or aliases is | |
1890 | allowed. | |
1891 | ||
1892 | Sometimes a host is not known to the translation function and | |
1893 | communication is blocked. To bypass this barrier two numeric | |
1894 | forms are also allowed for host "names". One form is a decimal | |
1895 | integer prefixed by a pound sign, "#", which indicates the | |
1896 | number is the address of the host. Another form is four small | |
1897 | decimal integers separated by dots and enclosed by brackets, | |
1898 | e.g., "[123.255.37.2]", which indicates a 32-bit ARPA Internet | |
1899 | Address in four 8-bit fields. | |
1900 | ||
1901 | ||
1902 | ||
1903 | Postel [Page 31] | |
1904 | \f | |
1905 | ||
1906 | ||
1907 | August 1982 RFC 821 | |
1908 | Simple Mail Transfer Protocol | |
1909 | ||
1910 | ||
1911 | ||
1912 | The time stamp line and the return path line are formally | |
1913 | defined as follows: | |
1914 | ||
1915 | <return-path-line> ::= "Return-Path:" <SP><reverse-path><CRLF> | |
1916 | ||
1917 | <time-stamp-line> ::= "Received:" <SP> <stamp> <CRLF> | |
1918 | ||
1919 | <stamp> ::= <from-domain> <by-domain> <opt-info> ";" | |
1920 | <daytime> | |
1921 | ||
1922 | <from-domain> ::= "FROM" <SP> <domain> <SP> | |
1923 | ||
1924 | <by-domain> ::= "BY" <SP> <domain> <SP> | |
1925 | ||
1926 | <opt-info> ::= [<via>] [<with>] [<id>] [<for>] | |
1927 | ||
1928 | <via> ::= "VIA" <SP> <link> <SP> | |
1929 | ||
1930 | <with> ::= "WITH" <SP> <protocol> <SP> | |
1931 | ||
1932 | <id> ::= "ID" <SP> <string> <SP> | |
1933 | ||
1934 | <for> ::= "FOR" <SP> <path> <SP> | |
1935 | ||
1936 | <link> ::= The standard names for links are registered with | |
1937 | the Network Information Center. | |
1938 | ||
1939 | <protocol> ::= The standard names for protocols are | |
1940 | registered with the Network Information Center. | |
1941 | ||
1942 | <daytime> ::= <SP> <date> <SP> <time> | |
1943 | ||
1944 | <date> ::= <dd> <SP> <mon> <SP> <yy> | |
1945 | ||
1946 | <time> ::= <hh> ":" <mm> ":" <ss> <SP> <zone> | |
1947 | ||
1948 | <dd> ::= the one or two decimal integer day of the month in | |
1949 | the range 1 to 31. | |
1950 | ||
1951 | <mon> ::= "JAN" | "FEB" | "MAR" | "APR" | "MAY" | "JUN" | | |
1952 | "JUL" | "AUG" | "SEP" | "OCT" | "NOV" | "DEC" | |
1953 | ||
1954 | <yy> ::= the two decimal integer year of the century in the | |
1955 | range 00 to 99. | |
1956 | ||
1957 | ||
1958 | ||
1959 | ||
1960 | ||
1961 | [Page 32] Postel | |
1962 | \f | |
1963 | ||
1964 | ||
1965 | RFC 821 August 1982 | |
1966 | Simple Mail Transfer Protocol | |
1967 | ||
1968 | ||
1969 | ||
1970 | <hh> ::= the two decimal integer hour of the day in the | |
1971 | range 00 to 24. | |
1972 | ||
1973 | <mm> ::= the two decimal integer minute of the hour in the | |
1974 | range 00 to 59. | |
1975 | ||
1976 | <ss> ::= the two decimal integer second of the minute in the | |
1977 | range 00 to 59. | |
1978 | ||
1979 | <zone> ::= "UT" for Universal Time (the default) or other | |
1980 | time zone designator (as in [2]). | |
1981 | ||
1982 | ||
1983 | ||
1984 | ------------------------------------------------------------- | |
1985 | ||
1986 | Return Path Example | |
1987 | ||
1988 | Return-Path: <@CHARLIE.ARPA,@BAKER.ARPA:JOE@ABLE.ARPA> | |
1989 | ||
1990 | Example 9 | |
1991 | ||
1992 | ------------------------------------------------------------- | |
1993 | ||
1994 | ------------------------------------------------------------- | |
1995 | ||
1996 | Time Stamp Line Example | |
1997 | ||
1998 | Received: FROM ABC.ARPA BY XYZ.ARPA ; 22 OCT 81 09:23:59 PDT | |
1999 | ||
2000 | Received: from ABC.ARPA by XYZ.ARPA via TELENET with X25 | |
2001 | id M12345 for Smith@PDQ.ARPA ; 22 OCT 81 09:23:59 PDT | |
2002 | ||
2003 | Example 10 | |
2004 | ||
2005 | ------------------------------------------------------------- | |
2006 | ||
2007 | ||
2008 | ||
2009 | ||
2010 | ||
2011 | ||
2012 | ||
2013 | ||
2014 | ||
2015 | ||
2016 | ||
2017 | ||
2018 | ||
2019 | Postel [Page 33] | |
2020 | \f | |
2021 | ||
2022 | ||
2023 | August 1982 RFC 821 | |
2024 | Simple Mail Transfer Protocol | |
2025 | ||
2026 | ||
2027 | ||
2028 | 4.2. SMTP REPLIES | |
2029 | ||
2030 | Replies to SMTP commands are devised to ensure the synchronization | |
2031 | of requests and actions in the process of mail transfer, and to | |
2032 | guarantee that the sender-SMTP always knows the state of the | |
2033 | receiver-SMTP. Every command must generate exactly one reply. | |
2034 | ||
2035 | The details of the command-reply sequence are made explicit in | |
2036 | Section 5.3 on Sequencing and Section 5.4 State Diagrams. | |
2037 | ||
2038 | An SMTP reply consists of a three digit number (transmitted as | |
2039 | three alphanumeric characters) followed by some text. The number | |
2040 | is intended for use by automata to determine what state to enter | |
2041 | next; the text is meant for the human user. It is intended that | |
2042 | the three digits contain enough encoded information that the | |
2043 | sender-SMTP need not examine the text and may either discard it or | |
2044 | pass it on to the user, as appropriate. In particular, the text | |
2045 | may be receiver-dependent and context dependent, so there are | |
2046 | likely to be varying texts for each reply code. A discussion of | |
2047 | the theory of reply codes is given in Appendix E. Formally, a | |
2048 | reply is defined to be the sequence: a three-digit code, <SP>, | |
2049 | one line of text, and <CRLF>, or a multiline reply (as defined in | |
2050 | Appendix E). Only the EXPN and HELP commands are expected to | |
2051 | result in multiline replies in normal circumstances, however | |
2052 | multiline replies are allowed for any command. | |
2053 | ||
2054 | ||
2055 | ||
2056 | ||
2057 | ||
2058 | ||
2059 | ||
2060 | ||
2061 | ||
2062 | ||
2063 | ||
2064 | ||
2065 | ||
2066 | ||
2067 | ||
2068 | ||
2069 | ||
2070 | ||
2071 | ||
2072 | ||
2073 | ||
2074 | ||
2075 | ||
2076 | ||
2077 | [Page 34] Postel | |
2078 | \f | |
2079 | ||
2080 | ||
2081 | RFC 821 August 1982 | |
2082 | Simple Mail Transfer Protocol | |
2083 | ||
2084 | ||
2085 | ||
2086 | 4.2.1. REPLY CODES BY FUNCTION GROUPS | |
2087 | ||
2088 | 500 Syntax error, command unrecognized | |
2089 | [This may include errors such as command line too long] | |
2090 | 501 Syntax error in parameters or arguments | |
2091 | 502 Command not implemented | |
2092 | 503 Bad sequence of commands | |
2093 | 504 Command parameter not implemented | |
2094 | ||
2095 | 211 System status, or system help reply | |
2096 | 214 Help message | |
2097 | [Information on how to use the receiver or the meaning of a | |
2098 | particular non-standard command; this reply is useful only | |
2099 | to the human user] | |
2100 | ||
2101 | 220 <domain> Service ready | |
2102 | 221 <domain> Service closing transmission channel | |
2103 | 421 <domain> Service not available, | |
2104 | closing transmission channel | |
2105 | [This may be a reply to any command if the service knows it | |
2106 | must shut down] | |
2107 | ||
2108 | 250 Requested mail action okay, completed | |
2109 | 251 User not local; will forward to <forward-path> | |
2110 | 450 Requested mail action not taken: mailbox unavailable | |
2111 | [E.g., mailbox busy] | |
2112 | 550 Requested action not taken: mailbox unavailable | |
2113 | [E.g., mailbox not found, no access] | |
2114 | 451 Requested action aborted: error in processing | |
2115 | 551 User not local; please try <forward-path> | |
2116 | 452 Requested action not taken: insufficient system storage | |
2117 | 552 Requested mail action aborted: exceeded storage allocation | |
2118 | 553 Requested action not taken: mailbox name not allowed | |
2119 | [E.g., mailbox syntax incorrect] | |
2120 | 354 Start mail input; end with <CRLF>.<CRLF> | |
2121 | 554 Transaction failed | |
2122 | ||
2123 | ||
2124 | ||
2125 | ||
2126 | ||
2127 | ||
2128 | ||
2129 | ||
2130 | ||
2131 | ||
2132 | ||
2133 | ||
2134 | ||
2135 | Postel [Page 35] | |
2136 | \f | |
2137 | ||
2138 | ||
2139 | August 1982 RFC 821 | |
2140 | Simple Mail Transfer Protocol | |
2141 | ||
2142 | ||
2143 | ||
2144 | 4.2.2. NUMERIC ORDER LIST OF REPLY CODES | |
2145 | ||
2146 | 211 System status, or system help reply | |
2147 | 214 Help message | |
2148 | [Information on how to use the receiver or the meaning of a | |
2149 | particular non-standard command; this reply is useful only | |
2150 | to the human user] | |
2151 | 220 <domain> Service ready | |
2152 | 221 <domain> Service closing transmission channel | |
2153 | 250 Requested mail action okay, completed | |
2154 | 251 User not local; will forward to <forward-path> | |
2155 | ||
2156 | 354 Start mail input; end with <CRLF>.<CRLF> | |
2157 | ||
2158 | 421 <domain> Service not available, | |
2159 | closing transmission channel | |
2160 | [This may be a reply to any command if the service knows it | |
2161 | must shut down] | |
2162 | 450 Requested mail action not taken: mailbox unavailable | |
2163 | [E.g., mailbox busy] | |
2164 | 451 Requested action aborted: local error in processing | |
2165 | 452 Requested action not taken: insufficient system storage | |
2166 | ||
2167 | 500 Syntax error, command unrecognized | |
2168 | [This may include errors such as command line too long] | |
2169 | 501 Syntax error in parameters or arguments | |
2170 | 502 Command not implemented | |
2171 | 503 Bad sequence of commands | |
2172 | 504 Command parameter not implemented | |
2173 | 550 Requested action not taken: mailbox unavailable | |
2174 | [E.g., mailbox not found, no access] | |
2175 | 551 User not local; please try <forward-path> | |
2176 | 552 Requested mail action aborted: exceeded storage allocation | |
2177 | 553 Requested action not taken: mailbox name not allowed | |
2178 | [E.g., mailbox syntax incorrect] | |
2179 | 554 Transaction failed | |
2180 | ||
2181 | ||
2182 | ||
2183 | ||
2184 | ||
2185 | ||
2186 | ||
2187 | ||
2188 | ||
2189 | ||
2190 | ||
2191 | ||
2192 | ||
2193 | [Page 36] Postel | |
2194 | \f | |
2195 | ||
2196 | ||
2197 | RFC 821 August 1982 | |
2198 | Simple Mail Transfer Protocol | |
2199 | ||
2200 | ||
2201 | ||
2202 | 4.3. SEQUENCING OF COMMANDS AND REPLIES | |
2203 | ||
2204 | The communication between the sender and receiver is intended to | |
2205 | be an alternating dialogue, controlled by the sender. As such, | |
2206 | the sender issues a command and the receiver responds with a | |
2207 | reply. The sender must wait for this response before sending | |
2208 | further commands. | |
2209 | ||
2210 | One important reply is the connection greeting. Normally, a | |
2211 | receiver will send a 220 "Service ready" reply when the connection | |
2212 | is completed. The sender should wait for this greeting message | |
2213 | before sending any commands. | |
2214 | ||
2215 | Note: all the greeting type replies have the official name of | |
2216 | the server host as the first word following the reply code. | |
2217 | ||
2218 | For example, | |
2219 | ||
2220 | 220 <SP> USC-ISIF.ARPA <SP> Service ready <CRLF> | |
2221 | ||
2222 | The table below lists alternative success and failure replies for | |
2223 | each command. These must be strictly adhered to; a receiver may | |
2224 | substitute text in the replies, but the meaning and action implied | |
2225 | by the code numbers and by the specific command reply sequence | |
2226 | cannot be altered. | |
2227 | ||
2228 | COMMAND-REPLY SEQUENCES | |
2229 | ||
2230 | Each command is listed with its possible replies. The prefixes | |
2231 | used before the possible replies are "P" for preliminary (not | |
2232 | used in SMTP), "I" for intermediate, "S" for success, "F" for | |
2233 | failure, and "E" for error. The 421 reply (service not | |
2234 | available, closing transmission channel) may be given to any | |
2235 | command if the SMTP-receiver knows it must shut down. This | |
2236 | listing forms the basis for the State Diagrams in Section 4.4. | |
2237 | ||
2238 | CONNECTION ESTABLISHMENT | |
2239 | S: 220 | |
2240 | F: 421 | |
2241 | HELO | |
2242 | S: 250 | |
2243 | E: 500, 501, 504, 421 | |
2244 | ||
2245 | S: 250 | |
2246 | F: 552, 451, 452 | |
2247 | E: 500, 501, 421 | |
2248 | ||
2249 | ||
2250 | ||
2251 | Postel [Page 37] | |
2252 | \f | |
2253 | ||
2254 | ||
2255 | August 1982 RFC 821 | |
2256 | Simple Mail Transfer Protocol | |
2257 | ||
2258 | ||
2259 | ||
2260 | RCPT | |
2261 | S: 250, 251 | |
2262 | F: 550, 551, 552, 553, 450, 451, 452 | |
2263 | E: 500, 501, 503, 421 | |
2264 | DATA | |
2265 | I: 354 -> data -> S: 250 | |
2266 | F: 552, 554, 451, 452 | |
2267 | F: 451, 554 | |
2268 | E: 500, 501, 503, 421 | |
2269 | RSET | |
2270 | S: 250 | |
2271 | E: 500, 501, 504, 421 | |
2272 | SEND | |
2273 | S: 250 | |
2274 | F: 552, 451, 452 | |
2275 | E: 500, 501, 502, 421 | |
2276 | SOML | |
2277 | S: 250 | |
2278 | F: 552, 451, 452 | |
2279 | E: 500, 501, 502, 421 | |
2280 | SAML | |
2281 | S: 250 | |
2282 | F: 552, 451, 452 | |
2283 | E: 500, 501, 502, 421 | |
2284 | VRFY | |
2285 | S: 250, 251 | |
2286 | F: 550, 551, 553 | |
2287 | E: 500, 501, 502, 504, 421 | |
2288 | EXPN | |
2289 | S: 250 | |
2290 | F: 550 | |
2291 | E: 500, 501, 502, 504, 421 | |
2292 | HELP | |
2293 | S: 211, 214 | |
2294 | E: 500, 501, 502, 504, 421 | |
2295 | NOOP | |
2296 | S: 250 | |
2297 | E: 500, 421 | |
2298 | QUIT | |
2299 | S: 221 | |
2300 | E: 500 | |
2301 | TURN | |
2302 | S: 250 | |
2303 | F: 502 | |
2304 | E: 500, 503 | |
2305 | ||
2306 | ||
2307 | ||
2308 | ||
2309 | [Page 38] Postel | |
2310 | \f | |
2311 | ||
2312 | ||
2313 | RFC 821 August 1982 | |
2314 | Simple Mail Transfer Protocol | |
2315 | ||
2316 | ||
2317 | ||
2318 | 4.4. STATE DIAGRAMS | |
2319 | ||
2320 | Following are state diagrams for a simple-minded SMTP | |
2321 | implementation. Only the first digit of the reply codes is used. | |
2322 | There is one state diagram for each group of SMTP commands. The | |
2323 | command groupings were determined by constructing a model for each | |
2324 | command and then collecting together the commands with | |
2325 | structurally identical models. | |
2326 | ||
2327 | For each command there are three possible outcomes: "success" | |
2328 | (S), "failure" (F), and "error" (E). In the state diagrams below | |
2329 | we use the symbol B for "begin", and the symbol W for "wait for | |
2330 | reply". | |
2331 | ||
2332 | First, the diagram that represents most of the SMTP commands: | |
2333 | ||
2334 | ||
2335 | 1,3 +---+ | |
2336 | ----------->| E | | |
2337 | | +---+ | |
2338 | | | |
2339 | +---+ cmd +---+ 2 +---+ | |
2340 | | B |---------->| W |---------->| S | | |
2341 | +---+ +---+ +---+ | |
2342 | | | |
2343 | | 4,5 +---+ | |
2344 | ----------->| F | | |
2345 | +---+ | |
2346 | ||
2347 | ||
2348 | This diagram models the commands: | |
2349 | ||
2350 | HELO, MAIL, RCPT, RSET, SEND, SOML, SAML, VRFY, EXPN, HELP, | |
2351 | NOOP, QUIT, TURN. | |
2352 | ||
2353 | ||
2354 | ||
2355 | ||
2356 | ||
2357 | ||
2358 | ||
2359 | ||
2360 | ||
2361 | ||
2362 | ||
2363 | ||
2364 | ||
2365 | ||
2366 | ||
2367 | Postel [Page 39] | |
2368 | \f | |
2369 | ||
2370 | ||
2371 | August 1982 RFC 821 | |
2372 | Simple Mail Transfer Protocol | |
2373 | ||
2374 | ||
2375 | ||
2376 | A more complex diagram models the DATA command: | |
2377 | ||
2378 | ||
2379 | +---+ DATA +---+ 1,2 +---+ | |
2380 | | B |---------->| W |-------------------->| E | | |
2381 | +---+ +---+ ------------>+---+ | |
2382 | 3| |4,5 | | |
2383 | | | | | |
2384 | -------------- ----- | | |
2385 | | | | +---+ | |
2386 | | ---------- -------->| S | | |
2387 | | | | | +---+ | |
2388 | | | ------------ | |
2389 | | | | | | |
2390 | V 1,3| |2 | | |
2391 | +---+ data +---+ --------------->+---+ | |
2392 | | |---------->| W | | F | | |
2393 | +---+ +---+-------------------->+---+ | |
2394 | 4,5 | |
2395 | ||
2396 | ||
2397 | Note that the "data" here is a series of lines sent from the | |
2398 | sender to the receiver with no response expected until the last | |
2399 | line is sent. | |
2400 | ||
2401 | ||
2402 | ||
2403 | ||
2404 | ||
2405 | ||
2406 | ||
2407 | ||
2408 | ||
2409 | ||
2410 | ||
2411 | ||
2412 | ||
2413 | ||
2414 | ||
2415 | ||
2416 | ||
2417 | ||
2418 | ||
2419 | ||
2420 | ||
2421 | ||
2422 | ||
2423 | ||
2424 | ||
2425 | [Page 40] Postel | |
2426 | \f | |
2427 | ||
2428 | ||
2429 | RFC 821 August 1982 | |
2430 | Simple Mail Transfer Protocol | |
2431 | ||
2432 | ||
2433 | ||
2434 | 4.5. DETAILS | |
2435 | ||
2436 | 4.5.1. MINIMUM IMPLEMENTATION | |
2437 | ||
2438 | In order to make SMTP workable, the following minimum | |
2439 | implementation is required for all receivers: | |
2440 | ||
2441 | COMMANDS -- HELO | |
2442 | ||
2443 | RCPT | |
2444 | DATA | |
2445 | RSET | |
2446 | NOOP | |
2447 | QUIT | |
2448 | ||
2449 | 4.5.2. TRANSPARENCY | |
2450 | ||
2451 | Without some provision for data transparency the character | |
2452 | sequence "<CRLF>.<CRLF>" ends the mail text and cannot be sent | |
2453 | by the user. In general, users are not aware of such | |
2454 | "forbidden" sequences. To allow all user composed text to be | |
2455 | transmitted transparently the following procedures are used. | |
2456 | ||
2457 | 1. Before sending a line of mail text the sender-SMTP checks | |
2458 | the first character of the line. If it is a period, one | |
2459 | additional period is inserted at the beginning of the line. | |
2460 | ||
2461 | 2. When a line of mail text is received by the receiver-SMTP | |
2462 | it checks the line. If the line is composed of a single | |
2463 | period it is the end of mail. If the first character is a | |
2464 | period and there are other characters on the line, the first | |
2465 | character is deleted. | |
2466 | ||
2467 | The mail data may contain any of the 128 ASCII characters. All | |
2468 | characters are to be delivered to the recipient's mailbox | |
2469 | including format effectors and other control characters. If | |
2470 | the transmission channel provides an 8-bit byte (octets) data | |
2471 | stream, the 7-bit ASCII codes are transmitted right justified | |
2472 | in the octets with the high order bits cleared to zero. | |
2473 | ||
2474 | In some systems it may be necessary to transform the data as | |
2475 | it is received and stored. This may be necessary for hosts | |
2476 | that use a different character set than ASCII as their local | |
2477 | character set, or that store data in records rather than | |
2478 | ||
2479 | ||
2480 | ||
2481 | ||
2482 | ||
2483 | Postel [Page 41] | |
2484 | \f | |
2485 | ||
2486 | ||
2487 | August 1982 RFC 821 | |
2488 | Simple Mail Transfer Protocol | |
2489 | ||
2490 | ||
2491 | ||
2492 | strings. If such transforms are necessary, they must be | |
2493 | reversible -- especially if such transforms are applied to | |
2494 | mail being relayed. | |
2495 | ||
2496 | 4.5.3. SIZES | |
2497 | ||
2498 | There are several objects that have required minimum maximum | |
2499 | sizes. That is, every implementation must be able to receive | |
2500 | objects of at least these sizes, but must not send objects | |
2501 | larger than these sizes. | |
2502 | ||
2503 | ||
2504 | **************************************************** | |
2505 | * * | |
2506 | * TO THE MAXIMUM EXTENT POSSIBLE, IMPLEMENTATION * | |
2507 | * TECHNIQUES WHICH IMPOSE NO LIMITS ON THE LENGTH * | |
2508 | * OF THESE OBJECTS SHOULD BE USED. * | |
2509 | * * | |
2510 | **************************************************** | |
2511 | ||
2512 | user | |
2513 | ||
2514 | The maximum total length of a user name is 64 characters. | |
2515 | ||
2516 | domain | |
2517 | ||
2518 | The maximum total length of a domain name or number is 64 | |
2519 | characters. | |
2520 | ||
2521 | path | |
2522 | ||
2523 | The maximum total length of a reverse-path or | |
2524 | forward-path is 256 characters (including the punctuation | |
2525 | and element separators). | |
2526 | ||
2527 | command line | |
2528 | ||
2529 | The maximum total length of a command line including the | |
2530 | command word and the <CRLF> is 512 characters. | |
2531 | ||
2532 | reply line | |
2533 | ||
2534 | The maximum total length of a reply line including the | |
2535 | reply code and the <CRLF> is 512 characters. | |
2536 | ||
2537 | ||
2538 | ||
2539 | ||
2540 | ||
2541 | [Page 42] Postel | |
2542 | \f | |
2543 | ||
2544 | ||
2545 | RFC 821 August 1982 | |
2546 | Simple Mail Transfer Protocol | |
2547 | ||
2548 | ||
2549 | ||
2550 | text line | |
2551 | ||
2552 | The maximum total length of a text line including the | |
2553 | <CRLF> is 1000 characters (but not counting the leading | |
2554 | dot duplicated for transparency). | |
2555 | ||
2556 | recipients buffer | |
2557 | ||
2558 | The maximum total number of recipients that must be | |
2559 | buffered is 100 recipients. | |
2560 | ||
2561 | ||
2562 | **************************************************** | |
2563 | * * | |
2564 | * TO THE MAXIMUM EXTENT POSSIBLE, IMPLEMENTATION * | |
2565 | * TECHNIQUES WHICH IMPOSE NO LIMITS ON THE LENGTH * | |
2566 | * OF THESE OBJECTS SHOULD BE USED. * | |
2567 | * * | |
2568 | **************************************************** | |
2569 | ||
2570 | Errors due to exceeding these limits may be reported by using | |
2571 | the reply codes, for example: | |
2572 | ||
2573 | 500 Line too long. | |
2574 | ||
2575 | 501 Path too long | |
2576 | ||
2577 | 552 Too many recipients. | |
2578 | ||
2579 | 552 Too much mail data. | |
2580 | ||
2581 | ||
2582 | ||
2583 | ||
2584 | ||
2585 | ||
2586 | ||
2587 | ||
2588 | ||
2589 | ||
2590 | ||
2591 | ||
2592 | ||
2593 | ||
2594 | ||
2595 | ||
2596 | ||
2597 | ||
2598 | ||
2599 | Postel [Page 43] | |
2600 | \f | |
2601 | ||
2602 | ||
2603 | August 1982 RFC 821 | |
2604 | Simple Mail Transfer Protocol | |
2605 | ||
2606 | ||
2607 | ||
2608 | APPENDIX A | |
2609 | ||
2610 | TCP Transport service | |
2611 | ||
2612 | The Transmission Control Protocol [3] is used in the ARPA | |
2613 | Internet, and in any network following the US DoD standards for | |
2614 | internetwork protocols. | |
2615 | ||
2616 | Connection Establishment | |
2617 | ||
2618 | The SMTP transmission channel is a TCP connection established | |
2619 | between the sender process port U and the receiver process port | |
2620 | L. This single full duplex connection is used as the | |
2621 | transmission channel. This protocol is assigned the service | |
2622 | port 25 (31 octal), that is L=25. | |
2623 | ||
2624 | Data Transfer | |
2625 | ||
2626 | The TCP connection supports the transmission of 8-bit bytes. | |
2627 | The SMTP data is 7-bit ASCII characters. Each character is | |
2628 | transmitted as an 8-bit byte with the high-order bit cleared to | |
2629 | zero. | |
2630 | ||
2631 | ||
2632 | ||
2633 | ||
2634 | ||
2635 | ||
2636 | ||
2637 | ||
2638 | ||
2639 | ||
2640 | ||
2641 | ||
2642 | ||
2643 | ||
2644 | ||
2645 | ||
2646 | ||
2647 | ||
2648 | ||
2649 | ||
2650 | ||
2651 | ||
2652 | ||
2653 | ||
2654 | ||
2655 | ||
2656 | ||
2657 | [Page 44] Postel | |
2658 | \f | |
2659 | ||
2660 | ||
2661 | RFC 821 August 1982 | |
2662 | Simple Mail Transfer Protocol | |
2663 | ||
2664 | ||
2665 | ||
2666 | APPENDIX B | |
2667 | ||
2668 | NCP Transport service | |
2669 | ||
2670 | The ARPANET Host-to-Host Protocol [4] (implemented by the Network | |
2671 | Control Program) may be used in the ARPANET. | |
2672 | ||
2673 | Connection Establishment | |
2674 | ||
2675 | The SMTP transmission channel is established via NCP between | |
2676 | the sender process socket U and receiver process socket L. The | |
2677 | Initial Connection Protocol [5] is followed resulting in a pair | |
2678 | of simplex connections. This pair of connections is used as | |
2679 | the transmission channel. This protocol is assigned the | |
2680 | contact socket 25 (31 octal), that is L=25. | |
2681 | ||
2682 | Data Transfer | |
2683 | ||
2684 | The NCP data connections are established in 8-bit byte mode. | |
2685 | The SMTP data is 7-bit ASCII characters. Each character is | |
2686 | transmitted as an 8-bit byte with the high-order bit cleared to | |
2687 | zero. | |
2688 | ||
2689 | ||
2690 | ||
2691 | ||
2692 | ||
2693 | ||
2694 | ||
2695 | ||
2696 | ||
2697 | ||
2698 | ||
2699 | ||
2700 | ||
2701 | ||
2702 | ||
2703 | ||
2704 | ||
2705 | ||
2706 | ||
2707 | ||
2708 | ||
2709 | ||
2710 | ||
2711 | ||
2712 | ||
2713 | ||
2714 | ||
2715 | Postel [Page 45] | |
2716 | \f | |
2717 | ||
2718 | ||
2719 | August 1982 RFC 821 | |
2720 | Simple Mail Transfer Protocol | |
2721 | ||
2722 | ||
2723 | ||
2724 | APPENDIX C | |
2725 | ||
2726 | NITS | |
2727 | ||
2728 | The Network Independent Transport Service [6] may be used. | |
2729 | ||
2730 | Connection Establishment | |
2731 | ||
2732 | The SMTP transmission channel is established via NITS between | |
2733 | the sender process and receiver process. The sender process | |
2734 | executes the CONNECT primitive, and the waiting receiver | |
2735 | process executes the ACCEPT primitive. | |
2736 | ||
2737 | Data Transfer | |
2738 | ||
2739 | The NITS connection supports the transmission of 8-bit bytes. | |
2740 | The SMTP data is 7-bit ASCII characters. Each character is | |
2741 | transmitted as an 8-bit byte with the high-order bit cleared to | |
2742 | zero. | |
2743 | ||
2744 | ||
2745 | ||
2746 | ||
2747 | ||
2748 | ||
2749 | ||
2750 | ||
2751 | ||
2752 | ||
2753 | ||
2754 | ||
2755 | ||
2756 | ||
2757 | ||
2758 | ||
2759 | ||
2760 | ||
2761 | ||
2762 | ||
2763 | ||
2764 | ||
2765 | ||
2766 | ||
2767 | ||
2768 | ||
2769 | ||
2770 | ||
2771 | ||
2772 | ||
2773 | [Page 46] Postel | |
2774 | \f | |
2775 | ||
2776 | ||
2777 | RFC 821 August 1982 | |
2778 | Simple Mail Transfer Protocol | |
2779 | ||
2780 | ||
2781 | ||
2782 | APPENDIX D | |
2783 | ||
2784 | X.25 Transport service | |
2785 | ||
2786 | It may be possible to use the X.25 service [7] as provided by the | |
2787 | Public Data Networks directly, however, it is suggested that a | |
2788 | reliable end-to-end protocol such as TCP be used on top of X.25 | |
2789 | connections. | |
2790 | ||
2791 | ||
2792 | ||
2793 | ||
2794 | ||
2795 | ||
2796 | ||
2797 | ||
2798 | ||
2799 | ||
2800 | ||
2801 | ||
2802 | ||
2803 | ||
2804 | ||
2805 | ||
2806 | ||
2807 | ||
2808 | ||
2809 | ||
2810 | ||
2811 | ||
2812 | ||
2813 | ||
2814 | ||
2815 | ||
2816 | ||
2817 | ||
2818 | ||
2819 | ||
2820 | ||
2821 | ||
2822 | ||
2823 | ||
2824 | ||
2825 | ||
2826 | ||
2827 | ||
2828 | ||
2829 | ||
2830 | ||
2831 | Postel [Page 47] | |
2832 | \f | |
2833 | ||
2834 | ||
2835 | August 1982 RFC 821 | |
2836 | Simple Mail Transfer Protocol | |
2837 | ||
2838 | ||
2839 | ||
2840 | APPENDIX E | |
2841 | ||
2842 | Theory of Reply Codes | |
2843 | ||
2844 | The three digits of the reply each have a special significance. | |
2845 | The first digit denotes whether the response is good, bad or | |
2846 | incomplete. An unsophisticated sender-SMTP will be able to | |
2847 | determine its next action (proceed as planned, redo, retrench, | |
2848 | etc.) by simply examining this first digit. A sender-SMTP that | |
2849 | wants to know approximately what kind of error occurred (e.g., | |
2850 | mail system error, command syntax error) may examine the second | |
2851 | digit, reserving the third digit for the finest gradation of | |
2852 | information. | |
2853 | ||
2854 | There are five values for the first digit of the reply code: | |
2855 | ||
2856 | 1yz Positive Preliminary reply | |
2857 | ||
2858 | The command has been accepted, but the requested action | |
2859 | is being held in abeyance, pending confirmation of the | |
2860 | information in this reply. The sender-SMTP should send | |
2861 | another command specifying whether to continue or abort | |
2862 | the action. | |
2863 | ||
2864 | [Note: SMTP does not have any commands that allow this | |
2865 | type of reply, and so does not have the continue or | |
2866 | abort commands.] | |
2867 | ||
2868 | 2yz Positive Completion reply | |
2869 | ||
2870 | The requested action has been successfully completed. A | |
2871 | new request may be initiated. | |
2872 | ||
2873 | 3yz Positive Intermediate reply | |
2874 | ||
2875 | The command has been accepted, but the requested action | |
2876 | is being held in abeyance, pending receipt of further | |
2877 | information. The sender-SMTP should send another command | |
2878 | specifying this information. This reply is used in | |
2879 | command sequence groups. | |
2880 | ||
2881 | 4yz Transient Negative Completion reply | |
2882 | ||
2883 | The command was not accepted and the requested action did | |
2884 | not occur. However, the error condition is temporary and | |
2885 | the action may be requested again. The sender should | |
2886 | ||
2887 | ||
2888 | ||
2889 | [Page 48] Postel | |
2890 | \f | |
2891 | ||
2892 | ||
2893 | RFC 821 August 1982 | |
2894 | Simple Mail Transfer Protocol | |
2895 | ||
2896 | ||
2897 | ||
2898 | return to the beginning of the command sequence (if any). | |
2899 | It is difficult to assign a meaning to "transient" when | |
2900 | two different sites (receiver- and sender- SMTPs) must | |
2901 | agree on the interpretation. Each reply in this category | |
2902 | might have a different time value, but the sender-SMTP is | |
2903 | encouraged to try again. A rule of thumb to determine if | |
2904 | a reply fits into the 4yz or the 5yz category (see below) | |
2905 | is that replies are 4yz if they can be repeated without | |
2906 | any change in command form or in properties of the sender | |
2907 | or receiver. (E.g., the command is repeated identically | |
2908 | and the receiver does not put up a new implementation.) | |
2909 | ||
2910 | 5yz Permanent Negative Completion reply | |
2911 | ||
2912 | The command was not accepted and the requested action did | |
2913 | not occur. The sender-SMTP is discouraged from repeating | |
2914 | the exact request (in the same sequence). Even some | |
2915 | "permanent" error conditions can be corrected, so the | |
2916 | human user may want to direct the sender-SMTP to | |
2917 | reinitiate the command sequence by direct action at some | |
2918 | point in the future (e.g., after the spelling has been | |
2919 | changed, or the user has altered the account status). | |
2920 | ||
2921 | The second digit encodes responses in specific categories: | |
2922 | ||
2923 | x0z Syntax -- These replies refer to syntax errors, | |
2924 | syntactically correct commands that don't fit any | |
2925 | functional category, and unimplemented or superfluous | |
2926 | commands. | |
2927 | ||
2928 | x1z Information -- These are replies to requests for | |
2929 | information, such as status or help. | |
2930 | ||
2931 | x2z Connections -- These are replies referring to the | |
2932 | transmission channel. | |
2933 | ||
2934 | x3z Unspecified as yet. | |
2935 | ||
2936 | x4z Unspecified as yet. | |
2937 | ||
2938 | x5z Mail system -- These replies indicate the status of | |
2939 | the receiver mail system vis-a-vis the requested | |
2940 | transfer or other mail system action. | |
2941 | ||
2942 | The third digit gives a finer gradation of meaning in each | |
2943 | category specified by the second digit. The list of replies | |
2944 | ||
2945 | ||
2946 | ||
2947 | Postel [Page 49] | |
2948 | \f | |
2949 | ||
2950 | ||
2951 | August 1982 RFC 821 | |
2952 | Simple Mail Transfer Protocol | |
2953 | ||
2954 | ||
2955 | ||
2956 | illustrates this. Each reply text is recommended rather than | |
2957 | mandatory, and may even change according to the command with | |
2958 | which it is associated. On the other hand, the reply codes | |
2959 | must strictly follow the specifications in this section. | |
2960 | Receiver implementations should not invent new codes for | |
2961 | slightly different situations from the ones described here, but | |
2962 | rather adapt codes already defined. | |
2963 | ||
2964 | For example, a command such as NOOP whose successful execution | |
2965 | does not offer the sender-SMTP any new information will return | |
2966 | a 250 reply. The response is 502 when the command requests an | |
2967 | unimplemented non-site-specific action. A refinement of that | |
2968 | is the 504 reply for a command that is implemented, but that | |
2969 | requests an unimplemented parameter. | |
2970 | ||
2971 | The reply text may be longer than a single line; in these cases | |
2972 | the complete text must be marked so the sender-SMTP knows when it | |
2973 | can stop reading the reply. This requires a special format to | |
2974 | indicate a multiple line reply. | |
2975 | ||
2976 | The format for multiline replies requires that every line, | |
2977 | except the last, begin with the reply code, followed | |
2978 | immediately by a hyphen, "-" (also known as minus), followed by | |
2979 | text. The last line will begin with the reply code, followed | |
2980 | immediately by <SP>, optionally some text, and <CRLF>. | |
2981 | ||
2982 | For example: | |
2983 | 123-First line | |
2984 | 123-Second line | |
2985 | 123-234 text beginning with numbers | |
2986 | 123 The last line | |
2987 | ||
2988 | In many cases the sender-SMTP then simply needs to search for | |
2989 | the reply code followed by <SP> at the beginning of a line, and | |
2990 | ignore all preceding lines. In a few cases, there is important | |
2991 | data for the sender in the reply "text". The sender will know | |
2992 | these cases from the current context. | |
2993 | ||
2994 | ||
2995 | ||
2996 | ||
2997 | ||
2998 | ||
2999 | ||
3000 | ||
3001 | ||
3002 | ||
3003 | ||
3004 | ||
3005 | [Page 50] Postel | |
3006 | \f | |
3007 | ||
3008 | ||
3009 | RFC 821 August 1982 | |
3010 | Simple Mail Transfer Protocol | |
3011 | ||
3012 | ||
3013 | ||
3014 | APPENDIX F | |
3015 | ||
3016 | Scenarios | |
3017 | ||
3018 | This section presents complete scenarios of several types of SMTP | |
3019 | sessions. | |
3020 | ||
3021 | A Typical SMTP Transaction Scenario | |
3022 | ||
3023 | This SMTP example shows mail sent by Smith at host USC-ISIF, to | |
3024 | Jones, Green, and Brown at host BBN-UNIX. Here we assume that | |
3025 | host USC-ISIF contacts host BBN-UNIX directly. The mail is | |
3026 | accepted for Jones and Brown. Green does not have a mailbox at | |
3027 | host BBN-UNIX. | |
3028 | ||
3029 | ------------------------------------------------------------- | |
3030 | ||
3031 | R: 220 BBN-UNIX.ARPA Simple Mail Transfer Service Ready | |
3032 | S: HELO USC-ISIF.ARPA | |
3033 | R: 250 BBN-UNIX.ARPA | |
3034 | ||
3035 | S: MAIL FROM:<Smith@USC-ISIF.ARPA> | |
3036 | R: 250 OK | |
3037 | ||
3038 | S: RCPT TO:<Jones@BBN-UNIX.ARPA> | |
3039 | R: 250 OK | |
3040 | ||
3041 | S: RCPT TO:<Green@BBN-UNIX.ARPA> | |
3042 | R: 550 No such user here | |
3043 | ||
3044 | S: RCPT TO:<Brown@BBN-UNIX.ARPA> | |
3045 | R: 250 OK | |
3046 | ||
3047 | S: DATA | |
3048 | R: 354 Start mail input; end with <CRLF>.<CRLF> | |
3049 | S: Blah blah blah... | |
3050 | S: ...etc. etc. etc. | |
3051 | S: . | |
3052 | R: 250 OK | |
3053 | ||
3054 | S: QUIT | |
3055 | R: 221 BBN-UNIX.ARPA Service closing transmission channel | |
3056 | ||
3057 | Scenario 1 | |
3058 | ||
3059 | ------------------------------------------------------------- | |
3060 | ||
3061 | ||
3062 | ||
3063 | Postel [Page 51] | |
3064 | \f | |
3065 | ||
3066 | ||
3067 | August 1982 RFC 821 | |
3068 | Simple Mail Transfer Protocol | |
3069 | ||
3070 | ||
3071 | ||
3072 | Aborted SMTP Transaction Scenario | |
3073 | ||
3074 | ------------------------------------------------------------- | |
3075 | ||
3076 | R: 220 MIT-Multics.ARPA Simple Mail Transfer Service Ready | |
3077 | S: HELO ISI-VAXA.ARPA | |
3078 | R: 250 MIT-Multics.ARPA | |
3079 | ||
3080 | S: MAIL FROM:<Smith@ISI-VAXA.ARPA> | |
3081 | R: 250 OK | |
3082 | ||
3083 | S: RCPT TO:<Jones@MIT-Multics.ARPA> | |
3084 | R: 250 OK | |
3085 | ||
3086 | S: RCPT TO:<Green@MIT-Multics.ARPA> | |
3087 | R: 550 No such user here | |
3088 | ||
3089 | S: RSET | |
3090 | R: 250 OK | |
3091 | ||
3092 | S: QUIT | |
3093 | R: 221 MIT-Multics.ARPA Service closing transmission channel | |
3094 | ||
3095 | Scenario 2 | |
3096 | ||
3097 | ------------------------------------------------------------- | |
3098 | ||
3099 | ||
3100 | ||
3101 | ||
3102 | ||
3103 | ||
3104 | ||
3105 | ||
3106 | ||
3107 | ||
3108 | ||
3109 | ||
3110 | ||
3111 | ||
3112 | ||
3113 | ||
3114 | ||
3115 | ||
3116 | ||
3117 | ||
3118 | ||
3119 | ||
3120 | ||
3121 | [Page 52] Postel | |
3122 | \f | |
3123 | ||
3124 | ||
3125 | RFC 821 August 1982 | |
3126 | Simple Mail Transfer Protocol | |
3127 | ||
3128 | ||
3129 | ||
3130 | Relayed Mail Scenario | |
3131 | ||
3132 | ------------------------------------------------------------- | |
3133 | ||
3134 | Step 1 -- Source Host to Relay Host | |
3135 | ||
3136 | R: 220 USC-ISIE.ARPA Simple Mail Transfer Service Ready | |
3137 | S: HELO MIT-AI.ARPA | |
3138 | R: 250 USC-ISIE.ARPA | |
3139 | ||
3140 | S: MAIL FROM:<JQP@MIT-AI.ARPA> | |
3141 | R: 250 OK | |
3142 | ||
3143 | S: RCPT TO:<@USC-ISIE.ARPA:Jones@BBN-VAX.ARPA> | |
3144 | R: 250 OK | |
3145 | ||
3146 | S: DATA | |
3147 | R: 354 Start mail input; end with <CRLF>.<CRLF> | |
3148 | S: Date: 2 Nov 81 22:33:44 | |
3149 | S: From: John Q. Public <JQP@MIT-AI.ARPA> | |
3150 | S: Subject: The Next Meeting of the Board | |
3151 | S: To: Jones@BBN-Vax.ARPA | |
3152 | S: | |
3153 | S: Bill: | |
3154 | S: The next meeting of the board of directors will be | |
3155 | S: on Tuesday. | |
3156 | S: John. | |
3157 | S: . | |
3158 | R: 250 OK | |
3159 | ||
3160 | S: QUIT | |
3161 | R: 221 USC-ISIE.ARPA Service closing transmission channel | |
3162 | ||
3163 | ||
3164 | ||
3165 | ||
3166 | ||
3167 | ||
3168 | ||
3169 | ||
3170 | ||
3171 | ||
3172 | ||
3173 | ||
3174 | ||
3175 | ||
3176 | ||
3177 | ||
3178 | ||
3179 | Postel [Page 53] | |
3180 | \f | |
3181 | ||
3182 | ||
3183 | August 1982 RFC 821 | |
3184 | Simple Mail Transfer Protocol | |
3185 | ||
3186 | ||
3187 | ||
3188 | Step 2 -- Relay Host to Destination Host | |
3189 | ||
3190 | R: 220 BBN-VAX.ARPA Simple Mail Transfer Service Ready | |
3191 | S: HELO USC-ISIE.ARPA | |
3192 | R: 250 BBN-VAX.ARPA | |
3193 | ||
3194 | S: MAIL FROM:<@USC-ISIE.ARPA:JQP@MIT-AI.ARPA> | |
3195 | R: 250 OK | |
3196 | ||
3197 | S: RCPT TO:<Jones@BBN-VAX.ARPA> | |
3198 | R: 250 OK | |
3199 | ||
3200 | S: DATA | |
3201 | R: 354 Start mail input; end with <CRLF>.<CRLF> | |
3202 | S: Received: from MIT-AI.ARPA by USC-ISIE.ARPA ; | |
3203 | 2 Nov 81 22:40:10 UT | |
3204 | S: Date: 2 Nov 81 22:33:44 | |
3205 | S: From: John Q. Public <JQP@MIT-AI.ARPA> | |
3206 | S: Subject: The Next Meeting of the Board | |
3207 | S: To: Jones@BBN-Vax.ARPA | |
3208 | S: | |
3209 | S: Bill: | |
3210 | S: The next meeting of the board of directors will be | |
3211 | S: on Tuesday. | |
3212 | S: John. | |
3213 | S: . | |
3214 | R: 250 OK | |
3215 | ||
3216 | S: QUIT | |
3217 | R: 221 USC-ISIE.ARPA Service closing transmission channel | |
3218 | ||
3219 | Scenario 3 | |
3220 | ||
3221 | ------------------------------------------------------------- | |
3222 | ||
3223 | ||
3224 | ||
3225 | ||
3226 | ||
3227 | ||
3228 | ||
3229 | ||
3230 | ||
3231 | ||
3232 | ||
3233 | ||
3234 | ||
3235 | ||
3236 | ||
3237 | [Page 54] Postel | |
3238 | \f | |
3239 | ||
3240 | ||
3241 | RFC 821 August 1982 | |
3242 | Simple Mail Transfer Protocol | |
3243 | ||
3244 | ||
3245 | ||
3246 | Verifying and Sending Scenario | |
3247 | ||
3248 | ------------------------------------------------------------- | |
3249 | ||
3250 | R: 220 SU-SCORE.ARPA Simple Mail Transfer Service Ready | |
3251 | S: HELO MIT-MC.ARPA | |
3252 | R: 250 SU-SCORE.ARPA | |
3253 | ||
3254 | S: VRFY Crispin | |
3255 | R: 250 Mark Crispin <Admin.MRC@SU-SCORE.ARPA> | |
3256 | ||
3257 | S: SEND FROM:<EAK@MIT-MC.ARPA> | |
3258 | R: 250 OK | |
3259 | ||
3260 | S: RCPT TO:<Admin.MRC@SU-SCORE.ARPA> | |
3261 | R: 250 OK | |
3262 | ||
3263 | S: DATA | |
3264 | R: 354 Start mail input; end with <CRLF>.<CRLF> | |
3265 | S: Blah blah blah... | |
3266 | S: ...etc. etc. etc. | |
3267 | S: . | |
3268 | R: 250 OK | |
3269 | ||
3270 | S: QUIT | |
3271 | R: 221 SU-SCORE.ARPA Service closing transmission channel | |
3272 | ||
3273 | Scenario 4 | |
3274 | ||
3275 | ------------------------------------------------------------- | |
3276 | ||
3277 | ||
3278 | ||
3279 | ||
3280 | ||
3281 | ||
3282 | ||
3283 | ||
3284 | ||
3285 | ||
3286 | ||
3287 | ||
3288 | ||
3289 | ||
3290 | ||
3291 | ||
3292 | ||
3293 | ||
3294 | ||
3295 | Postel [Page 55] | |
3296 | \f | |
3297 | ||
3298 | ||
3299 | August 1982 RFC 821 | |
3300 | Simple Mail Transfer Protocol | |
3301 | ||
3302 | ||
3303 | ||
3304 | Sending and Mailing Scenarios | |
3305 | ||
3306 | First the user's name is verified, then an attempt is made to | |
3307 | send to the user's terminal. When that fails, the messages is | |
3308 | mailed to the user's mailbox. | |
3309 | ||
3310 | ------------------------------------------------------------- | |
3311 | ||
3312 | R: 220 SU-SCORE.ARPA Simple Mail Transfer Service Ready | |
3313 | S: HELO MIT-MC.ARPA | |
3314 | R: 250 SU-SCORE.ARPA | |
3315 | ||
3316 | S: VRFY Crispin | |
3317 | R: 250 Mark Crispin <Admin.MRC@SU-SCORE.ARPA> | |
3318 | ||
3319 | S: SEND FROM:<EAK@MIT-MC.ARPA> | |
3320 | R: 250 OK | |
3321 | ||
3322 | S: RCPT TO:<Admin.MRC@SU-SCORE.ARPA> | |
3323 | R: 450 User not active now | |
3324 | ||
3325 | S: RSET | |
3326 | R: 250 OK | |
3327 | ||
3328 | S: MAIL FROM:<EAK@MIT-MC.ARPA> | |
3329 | R: 250 OK | |
3330 | ||
3331 | S: RCPT TO:<Admin.MRC@SU-SCORE.ARPA> | |
3332 | R: 250 OK | |
3333 | ||
3334 | S: DATA | |
3335 | R: 354 Start mail input; end with <CRLF>.<CRLF> | |
3336 | S: Blah blah blah... | |
3337 | S: ...etc. etc. etc. | |
3338 | S: . | |
3339 | R: 250 OK | |
3340 | ||
3341 | S: QUIT | |
3342 | R: 221 SU-SCORE.ARPA Service closing transmission channel | |
3343 | ||
3344 | Scenario 5 | |
3345 | ||
3346 | ------------------------------------------------------------- | |
3347 | ||
3348 | ||
3349 | ||
3350 | ||
3351 | ||
3352 | ||
3353 | [Page 56] Postel | |
3354 | \f | |
3355 | ||
3356 | ||
3357 | RFC 821 August 1982 | |
3358 | Simple Mail Transfer Protocol | |
3359 | ||
3360 | ||
3361 | ||
3362 | Doing the preceding scenario more efficiently. | |
3363 | ||
3364 | ------------------------------------------------------------- | |
3365 | ||
3366 | R: 220 SU-SCORE.ARPA Simple Mail Transfer Service Ready | |
3367 | S: HELO MIT-MC.ARPA | |
3368 | R: 250 SU-SCORE.ARPA | |
3369 | ||
3370 | S: VRFY Crispin | |
3371 | R: 250 Mark Crispin <Admin.MRC@SU-SCORE.ARPA> | |
3372 | ||
3373 | S: SOML FROM:<EAK@MIT-MC.ARPA> | |
3374 | R: 250 OK | |
3375 | ||
3376 | S: RCPT TO:<Admin.MRC@SU-SCORE.ARPA> | |
3377 | R: 250 User not active now, so will do mail. | |
3378 | ||
3379 | S: DATA | |
3380 | R: 354 Start mail input; end with <CRLF>.<CRLF> | |
3381 | S: Blah blah blah... | |
3382 | S: ...etc. etc. etc. | |
3383 | S: . | |
3384 | R: 250 OK | |
3385 | ||
3386 | S: QUIT | |
3387 | R: 221 SU-SCORE.ARPA Service closing transmission channel | |
3388 | ||
3389 | Scenario 6 | |
3390 | ||
3391 | ------------------------------------------------------------- | |
3392 | ||
3393 | ||
3394 | ||
3395 | ||
3396 | ||
3397 | ||
3398 | ||
3399 | ||
3400 | ||
3401 | ||
3402 | ||
3403 | ||
3404 | ||
3405 | ||
3406 | ||
3407 | ||
3408 | ||
3409 | ||
3410 | ||
3411 | Postel [Page 57] | |
3412 | \f | |
3413 | ||
3414 | ||
3415 | August 1982 RFC 821 | |
3416 | Simple Mail Transfer Protocol | |
3417 | ||
3418 | ||
3419 | ||
3420 | Mailing List Scenario | |
3421 | ||
3422 | First each of two mailing lists are expanded in separate sessions | |
3423 | with different hosts. Then the message is sent to everyone that | |
3424 | appeared on either list (but no duplicates) via a relay host. | |
3425 | ||
3426 | ------------------------------------------------------------- | |
3427 | ||
3428 | Step 1 -- Expanding the First List | |
3429 | ||
3430 | R: 220 MIT-AI.ARPA Simple Mail Transfer Service Ready | |
3431 | S: HELO SU-SCORE.ARPA | |
3432 | R: 250 MIT-AI.ARPA | |
3433 | ||
3434 | S: EXPN Example-People | |
3435 | R: 250-<ABC@MIT-MC.ARPA> | |
3436 | R: 250-Fred Fonebone <Fonebone@USC-ISIQ.ARPA> | |
3437 | R: 250-Xenon Y. Zither <XYZ@MIT-AI.ARPA> | |
3438 | R: 250-Quincy Smith <@USC-ISIF.ARPA:Q-Smith@ISI-VAXA.ARPA> | |
3439 | R: 250-<joe@foo-unix.ARPA> | |
3440 | R: 250 <xyz@bar-unix.ARPA> | |
3441 | ||
3442 | S: QUIT | |
3443 | R: 221 MIT-AI.ARPA Service closing transmission channel | |
3444 | ||
3445 | ||
3446 | ||
3447 | ||
3448 | ||
3449 | ||
3450 | ||
3451 | ||
3452 | ||
3453 | ||
3454 | ||
3455 | ||
3456 | ||
3457 | ||
3458 | ||
3459 | ||
3460 | ||
3461 | ||
3462 | ||
3463 | ||
3464 | ||
3465 | ||
3466 | ||
3467 | ||
3468 | ||
3469 | [Page 58] Postel | |
3470 | \f | |
3471 | ||
3472 | ||
3473 | RFC 821 August 1982 | |
3474 | Simple Mail Transfer Protocol | |
3475 | ||
3476 | ||
3477 | ||
3478 | Step 2 -- Expanding the Second List | |
3479 | ||
3480 | R: 220 MIT-MC.ARPA Simple Mail Transfer Service Ready | |
3481 | S: HELO SU-SCORE.ARPA | |
3482 | R: 250 MIT-MC.ARPA | |
3483 | ||
3484 | S: EXPN Interested-Parties | |
3485 | R: 250-Al Calico <ABC@MIT-MC.ARPA> | |
3486 | R: 250-<XYZ@MIT-AI.ARPA> | |
3487 | R: 250-Quincy Smith <@USC-ISIF.ARPA:Q-Smith@ISI-VAXA.ARPA> | |
3488 | R: 250-<fred@BBN-UNIX.ARPA> | |
3489 | R: 250 <xyz@bar-unix.ARPA> | |
3490 | ||
3491 | S: QUIT | |
3492 | R: 221 MIT-MC.ARPA Service closing transmission channel | |
3493 | ||
3494 | ||
3495 | ||
3496 | ||
3497 | ||
3498 | ||
3499 | ||
3500 | ||
3501 | ||
3502 | ||
3503 | ||
3504 | ||
3505 | ||
3506 | ||
3507 | ||
3508 | ||
3509 | ||
3510 | ||
3511 | ||
3512 | ||
3513 | ||
3514 | ||
3515 | ||
3516 | ||
3517 | ||
3518 | ||
3519 | ||
3520 | ||
3521 | ||
3522 | ||
3523 | ||
3524 | ||
3525 | ||
3526 | ||
3527 | Postel [Page 59] | |
3528 | \f | |
3529 | ||
3530 | ||
3531 | August 1982 RFC 821 | |
3532 | Simple Mail Transfer Protocol | |
3533 | ||
3534 | ||
3535 | ||
3536 | Step 3 -- Mailing to All via a Relay Host | |
3537 | ||
3538 | R: 220 USC-ISIE.ARPA Simple Mail Transfer Service Ready | |
3539 | S: HELO SU-SCORE.ARPA | |
3540 | R: 250 USC-ISIE.ARPA | |
3541 | ||
3542 | S: MAIL FROM:<Account.Person@SU-SCORE.ARPA> | |
3543 | R: 250 OK | |
3544 | S: RCPT TO:<@USC-ISIE.ARPA:ABC@MIT-MC.ARPA> | |
3545 | R: 250 OK | |
3546 | S: RCPT TO:<@USC-ISIE.ARPA:Fonebone@USC-ISIQA.ARPA> | |
3547 | R: 250 OK | |
3548 | S: RCPT TO:<@USC-ISIE.ARPA:XYZ@MIT-AI.ARPA> | |
3549 | R: 250 OK | |
3550 | S: RCPT | |
3551 | TO:<@USC-ISIE.ARPA,@USC-ISIF.ARPA:Q-Smith@ISI-VAXA.ARPA> | |
3552 | R: 250 OK | |
3553 | S: RCPT TO:<@USC-ISIE.ARPA:joe@FOO-UNIX.ARPA> | |
3554 | R: 250 OK | |
3555 | S: RCPT TO:<@USC-ISIE.ARPA:xyz@BAR-UNIX.ARPA> | |
3556 | R: 250 OK | |
3557 | S: RCPT TO:<@USC-ISIE.ARPA:fred@BBN-UNIX.ARPA> | |
3558 | R: 250 OK | |
3559 | ||
3560 | S: DATA | |
3561 | R: 354 Start mail input; end with <CRLF>.<CRLF> | |
3562 | S: Blah blah blah... | |
3563 | S: ...etc. etc. etc. | |
3564 | S: . | |
3565 | R: 250 OK | |
3566 | ||
3567 | S: QUIT | |
3568 | R: 221 USC-ISIE.ARPA Service closing transmission channel | |
3569 | ||
3570 | Scenario 7 | |
3571 | ||
3572 | ------------------------------------------------------------- | |
3573 | ||
3574 | ||
3575 | ||
3576 | ||
3577 | ||
3578 | ||
3579 | ||
3580 | ||
3581 | ||
3582 | ||
3583 | ||
3584 | ||
3585 | [Page 60] Postel | |
3586 | \f | |
3587 | ||
3588 | ||
3589 | RFC 821 August 1982 | |
3590 | Simple Mail Transfer Protocol | |
3591 | ||
3592 | ||
3593 | ||
3594 | Forwarding Scenarios | |
3595 | ||
3596 | ------------------------------------------------------------- | |
3597 | ||
3598 | R: 220 USC-ISIF.ARPA Simple Mail Transfer Service Ready | |
3599 | S: HELO LBL-UNIX.ARPA | |
3600 | R: 250 USC-ISIF.ARPA | |
3601 | ||
3602 | S: MAIL FROM:<mo@LBL-UNIX.ARPA> | |
3603 | R: 250 OK | |
3604 | ||
3605 | S: RCPT TO:<fred@USC-ISIF.ARPA> | |
3606 | R: 251 User not local; will forward to <Jones@USC-ISI.ARPA> | |
3607 | ||
3608 | S: DATA | |
3609 | R: 354 Start mail input; end with <CRLF>.<CRLF> | |
3610 | S: Blah blah blah... | |
3611 | S: ...etc. etc. etc. | |
3612 | S: . | |
3613 | R: 250 OK | |
3614 | ||
3615 | S: QUIT | |
3616 | R: 221 USC-ISIF.ARPA Service closing transmission channel | |
3617 | ||
3618 | Scenario 8 | |
3619 | ||
3620 | ------------------------------------------------------------- | |
3621 | ||
3622 | ||
3623 | ||
3624 | ||
3625 | ||
3626 | ||
3627 | ||
3628 | ||
3629 | ||
3630 | ||
3631 | ||
3632 | ||
3633 | ||
3634 | ||
3635 | ||
3636 | ||
3637 | ||
3638 | ||
3639 | ||
3640 | ||
3641 | ||
3642 | ||
3643 | Postel [Page 61] | |
3644 | \f | |
3645 | ||
3646 | ||
3647 | August 1982 RFC 821 | |
3648 | Simple Mail Transfer Protocol | |
3649 | ||
3650 | ||
3651 | ||
3652 | ------------------------------------------------------------- | |
3653 | ||
3654 | Step 1 -- Trying the Mailbox at the First Host | |
3655 | ||
3656 | R: 220 USC-ISIF.ARPA Simple Mail Transfer Service Ready | |
3657 | S: HELO LBL-UNIX.ARPA | |
3658 | R: 250 USC-ISIF.ARPA | |
3659 | ||
3660 | S: MAIL FROM:<mo@LBL-UNIX.ARPA> | |
3661 | R: 250 OK | |
3662 | ||
3663 | S: RCPT TO:<fred@USC-ISIF.ARPA> | |
3664 | R: 251 User not local; will forward to <Jones@USC-ISI.ARPA> | |
3665 | ||
3666 | S: RSET | |
3667 | R: 250 OK | |
3668 | ||
3669 | S: QUIT | |
3670 | R: 221 USC-ISIF.ARPA Service closing transmission channel | |
3671 | ||
3672 | Step 2 -- Delivering the Mail at the Second Host | |
3673 | ||
3674 | R: 220 USC-ISI.ARPA Simple Mail Transfer Service Ready | |
3675 | S: HELO LBL-UNIX.ARPA | |
3676 | R: 250 USC-ISI.ARPA | |
3677 | ||
3678 | S: MAIL FROM:<mo@LBL-UNIX.ARPA> | |
3679 | R: 250 OK | |
3680 | ||
3681 | S: RCPT TO:<Jones@USC-ISI.ARPA> | |
3682 | R: OK | |
3683 | ||
3684 | S: DATA | |
3685 | R: 354 Start mail input; end with <CRLF>.<CRLF> | |
3686 | S: Blah blah blah... | |
3687 | S: ...etc. etc. etc. | |
3688 | S: . | |
3689 | R: 250 OK | |
3690 | ||
3691 | S: QUIT | |
3692 | R: 221 USC-ISI.ARPA Service closing transmission channel | |
3693 | ||
3694 | Scenario 9 | |
3695 | ||
3696 | ------------------------------------------------------------- | |
3697 | ||
3698 | ||
3699 | ||
3700 | ||
3701 | [Page 62] Postel | |
3702 | \f | |
3703 | ||
3704 | ||
3705 | RFC 821 August 1982 | |
3706 | Simple Mail Transfer Protocol | |
3707 | ||
3708 | ||
3709 | ||
3710 | Too Many Recipients Scenario | |
3711 | ||
3712 | ------------------------------------------------------------- | |
3713 | ||
3714 | R: 220 BERKELEY.ARPA Simple Mail Transfer Service Ready | |
3715 | S: HELO USC-ISIF.ARPA | |
3716 | R: 250 BERKELEY.ARPA | |
3717 | ||
3718 | S: MAIL FROM:<Postel@USC-ISIF.ARPA> | |
3719 | R: 250 OK | |
3720 | ||
3721 | S: RCPT TO:<fabry@BERKELEY.ARPA> | |
3722 | R: 250 OK | |
3723 | ||
3724 | S: RCPT TO:<eric@BERKELEY.ARPA> | |
3725 | R: 552 Recipient storage full, try again in another transaction | |
3726 | ||
3727 | S: DATA | |
3728 | R: 354 Start mail input; end with <CRLF>.<CRLF> | |
3729 | S: Blah blah blah... | |
3730 | S: ...etc. etc. etc. | |
3731 | S: . | |
3732 | R: 250 OK | |
3733 | ||
3734 | S: MAIL FROM:<Postel@USC-ISIF.ARPA> | |
3735 | R: 250 OK | |
3736 | ||
3737 | S: RCPT TO:<eric@BERKELEY.ARPA> | |
3738 | R: 250 OK | |
3739 | ||
3740 | S: DATA | |
3741 | R: 354 Start mail input; end with <CRLF>.<CRLF> | |
3742 | S: Blah blah blah... | |
3743 | S: ...etc. etc. etc. | |
3744 | S: . | |
3745 | R: 250 OK | |
3746 | ||
3747 | S: QUIT | |
3748 | R: 221 BERKELEY.ARPA Service closing transmission channel | |
3749 | ||
3750 | Scenario 10 | |
3751 | ||
3752 | ------------------------------------------------------------- | |
3753 | ||
3754 | Note that a real implementation must handle many recipients as | |
3755 | specified in Section 4.5.3. | |
3756 | ||
3757 | ||
3758 | ||
3759 | Postel [Page 63] | |
3760 | \f | |
3761 | ||
3762 | ||
3763 | August 1982 RFC 821 | |
3764 | Simple Mail Transfer Protocol | |
3765 | ||
3766 | ||
3767 | ||
3768 | GLOSSARY | |
3769 | ||
3770 | ASCII | |
3771 | ||
3772 | American Standard Code for Information Interchange [1]. | |
3773 | ||
3774 | command | |
3775 | ||
3776 | A request for a mail service action sent by the sender-SMTP to the | |
3777 | receiver-SMTP. | |
3778 | ||
3779 | domain | |
3780 | ||
3781 | The hierarchially structured global character string address of a | |
3782 | host computer in the mail system. | |
3783 | ||
3784 | end of mail data indication | |
3785 | ||
3786 | A special sequence of characters that indicates the end of the | |
3787 | mail data. In particular, the five characters carriage return, | |
3788 | line feed, period, carriage return, line feed, in that order. | |
3789 | ||
3790 | host | |
3791 | ||
3792 | A computer in the internetwork environment on which mailboxes or | |
3793 | SMTP processes reside. | |
3794 | ||
3795 | line | |
3796 | ||
3797 | A a sequence of ASCII characters ending with a <CRLF>. | |
3798 | ||
3799 | mail data | |
3800 | ||
3801 | A sequence of ASCII characters of arbitrary length, which conforms | |
3802 | to the standard set in the Standard for the Format of ARPA | |
3803 | Internet Text Messages (RFC 822 [2]). | |
3804 | ||
3805 | mailbox | |
3806 | ||
3807 | A character string (address) which identifies a user to whom mail | |
3808 | is to be sent. Mailbox normally consists of the host and user | |
3809 | specifications. The standard mailbox naming convention is defined | |
3810 | to be "user@domain". Additionally, the "container" in which mail | |
3811 | is stored. | |
3812 | ||
3813 | ||
3814 | ||
3815 | ||
3816 | ||
3817 | [Page 64] Postel | |
3818 | \f | |
3819 | ||
3820 | ||
3821 | RFC 821 August 1982 | |
3822 | Simple Mail Transfer Protocol | |
3823 | ||
3824 | ||
3825 | ||
3826 | receiver-SMTP process | |
3827 | ||
3828 | A process which transfers mail in cooperation with a sender-SMTP | |
3829 | process. It waits for a connection to be established via the | |
3830 | transport service. It receives SMTP commands from the | |
3831 | sender-SMTP, sends replies, and performs the specified operations. | |
3832 | ||
3833 | reply | |
3834 | ||
3835 | A reply is an acknowledgment (positive or negative) sent from | |
3836 | receiver to sender via the transmission channel in response to a | |
3837 | command. The general form of a reply is a completion code | |
3838 | (including error codes) followed by a text string. The codes are | |
3839 | for use by programs and the text is usually intended for human | |
3840 | users. | |
3841 | ||
3842 | sender-SMTP process | |
3843 | ||
3844 | A process which transfers mail in cooperation with a receiver-SMTP | |
3845 | process. A local language may be used in the user interface | |
3846 | command/reply dialogue. The sender-SMTP initiates the transport | |
3847 | service connection. It initiates SMTP commands, receives replies, | |
3848 | and governs the transfer of mail. | |
3849 | ||
3850 | session | |
3851 | ||
3852 | The set of exchanges that occur while the transmission channel is | |
3853 | open. | |
3854 | ||
3855 | transaction | |
3856 | ||
3857 | The set of exchanges required for one message to be transmitted | |
3858 | for one or more recipients. | |
3859 | ||
3860 | transmission channel | |
3861 | ||
3862 | A full-duplex communication path between a sender-SMTP and a | |
3863 | receiver-SMTP for the exchange of commands, replies, and mail | |
3864 | text. | |
3865 | ||
3866 | transport service | |
3867 | ||
3868 | Any reliable stream-oriented data communication services. For | |
3869 | example, NCP, TCP, NITS. | |
3870 | ||
3871 | ||
3872 | ||
3873 | ||
3874 | ||
3875 | Postel [Page 65] | |
3876 | \f | |
3877 | ||
3878 | ||
3879 | August 1982 RFC 821 | |
3880 | Simple Mail Transfer Protocol | |
3881 | ||
3882 | ||
3883 | ||
3884 | user | |
3885 | ||
3886 | A human being (or a process on behalf of a human being) wishing to | |
3887 | obtain mail transfer service. In addition, a recipient of | |
3888 | computer mail. | |
3889 | ||
3890 | word | |
3891 | ||
3892 | A sequence of printing characters. | |
3893 | ||
3894 | <CRLF> | |
3895 | ||
3896 | The characters carriage return and line feed (in that order). | |
3897 | ||
3898 | <SP> | |
3899 | ||
3900 | The space character. | |
3901 | ||
3902 | ||
3903 | ||
3904 | ||
3905 | ||
3906 | ||
3907 | ||
3908 | ||
3909 | ||
3910 | ||
3911 | ||
3912 | ||
3913 | ||
3914 | ||
3915 | ||
3916 | ||
3917 | ||
3918 | ||
3919 | ||
3920 | ||
3921 | ||
3922 | ||
3923 | ||
3924 | ||
3925 | ||
3926 | ||
3927 | ||
3928 | ||
3929 | ||
3930 | ||
3931 | ||
3932 | ||
3933 | [Page 66] Postel | |
3934 | \f | |
3935 | ||
3936 | ||
3937 | RFC 821 August 1982 | |
3938 | Simple Mail Transfer Protocol | |
3939 | ||
3940 | ||
3941 | ||
3942 | REFERENCES | |
3943 | ||
3944 | [1] ASCII | |
3945 | ||
3946 | ASCII, "USA Code for Information Interchange", United States of | |
3947 | America Standards Institute, X3.4, 1968. Also in: Feinler, E. | |
3948 | and J. Postel, eds., "ARPANET Protocol Handbook", NIC 7104, for | |
3949 | the Defense Communications Agency by SRI International, Menlo | |
3950 | Park, California, Revised January 1978. | |
3951 | ||
3952 | [2] RFC 822 | |
3953 | ||
3954 | Crocker, D., "Standard for the Format of ARPA Internet Text | |
3955 | Messages," RFC 822, Department of Electrical Engineering, | |
3956 | University of Delaware, August 1982. | |
3957 | ||
3958 | [3] TCP | |
3959 | ||
3960 | Postel, J., ed., "Transmission Control Protocol - DARPA Internet | |
3961 | Program Protocol Specification", RFC 793, USC/Information Sciences | |
3962 | Institute, NTIS AD Number A111091, September 1981. Also in: | |
3963 | Feinler, E. and J. Postel, eds., "Internet Protocol Transition | |
3964 | Workbook", SRI International, Menlo Park, California, March 1982. | |
3965 | ||
3966 | [4] NCP | |
3967 | ||
3968 | McKenzie,A., "Host/Host Protocol for the ARPA Network", NIC 8246, | |
3969 | January 1972. Also in: Feinler, E. and J. Postel, eds., "ARPANET | |
3970 | Protocol Handbook", NIC 7104, for the Defense Communications | |
3971 | Agency by SRI International, Menlo Park, California, Revised | |
3972 | January 1978. | |
3973 | ||
3974 | [5] Initial Connection Protocol | |
3975 | ||
3976 | Postel, J., "Official Initial Connection Protocol", NIC 7101, | |
3977 | 11 June 1971. Also in: Feinler, E. and J. Postel, eds., "ARPANET | |
3978 | Protocol Handbook", NIC 7104, for the Defense Communications | |
3979 | Agency by SRI International, Menlo Park, California, Revised | |
3980 | January 1978. | |
3981 | ||
3982 | [6] NITS | |
3983 | ||
3984 | PSS/SG3, "A Network Independent Transport Service", Study Group 3, | |
3985 | The Post Office PSS Users Group, February 1980. Available from | |
3986 | the DCPU, National Physical Laboratory, Teddington, UK. | |
3987 | ||
3988 | ||
3989 | ||
3990 | ||
3991 | Postel [Page 67] | |
3992 | \f | |
3993 | ||
3994 | ||
3995 | August 1982 RFC 821 | |
3996 | Simple Mail Transfer Protocol | |
3997 | ||
3998 | ||
3999 | ||
4000 | [7] X.25 | |
4001 | ||
4002 | CCITT, "Recommendation X.25 - Interface Between Data Terminal | |
4003 | Equipment (DTE) and Data Circuit-terminating Equipment (DCE) for | |
4004 | Terminals Operating in the Packet Mode on Public Data Networks," | |
4005 | CCITT Orange Book, Vol. VIII.2, International Telephone and | |
4006 | Telegraph Consultative Committee, Geneva, 1976. | |
4007 | ||
4008 | ||
4009 | ||
4010 | ||
4011 | ||
4012 | ||
4013 | ||
4014 | ||
4015 | ||
4016 | ||
4017 | ||
4018 | ||
4019 | ||
4020 | ||
4021 | ||
4022 | ||
4023 | ||
4024 | ||
4025 | ||
4026 | ||
4027 | ||
4028 | ||
4029 | ||
4030 | ||
4031 | ||
4032 | ||
4033 | ||
4034 | ||
4035 | ||
4036 | ||
4037 | ||
4038 | ||
4039 | ||
4040 | ||
4041 | ||
4042 | ||
4043 | ||
4044 | ||
4045 | ||
4046 | ||
4047 | ||
4048 | ||
4049 | [Page 68] Postel | |
4050 | \f |