+.\" @(#)mailaddr.7 3.1 %G%
+.TH MAILADDR 7
+.UC 4
+.SH NAME
+mailaddr \- mail addressing description
+.SH DESCRIPTION
+Mail addresses are based on the ARPANET protocols
+listed at the end of this manual page.
+These addresses are in the general format
+.PP
+ user@domain
+.PP
+where a domain is a hierarchical dot separated list of subdomains.
+For example,
+the address
+.PP
+ eric@monet.Berkeley.ARPA
+.PP
+is normally interpreted from right to left:
+the message should go to the ARPA name tables
+(which do not correspond exactly to the physical ARPANET),
+then to the Berkeley gateway,
+after which it should go to the local host monet.
+When the message reaches monet it is delivered to the user ``eric''.
+.PP
+Unlike some other forms of addressing,
+this does not imply any routing.
+Thus,
+although this address is specified as an ARPA address,
+it might travel by an alternate route
+if that was more convenient or efficient.
+For example,
+at Berkeley the associated message
+would probably go directly to monet over the Ethernet
+rather than going via the Berkeley ARPANET gateway.
+.PP
+.I Abbreviation.
+Under certain circumstances
+it may not be necessary to type the entire domain name.
+In general anything following the first dot
+may be omitted
+if it is the same as the domain from which you are sending the message.
+For example,
+a user on
+``calder.Berkeley.ARPA''
+could send to
+``eric@monet''
+without adding the
+``.Berkeley.ARPA''
+since it is the same on both sending and receiving hosts.
+.PP
+Certain other abbreviations may be permitted
+as special cases.
+For example,
+at Berkeley ARPANET hosts can be referenced
+without adding the
+``.ARPA''
+as long as their names do not conflict
+with a local host name.
+.PP
+.I Compatibility.
+Certain old address formats
+are converted to the new format
+to provide compatibility with the previous mail system.
+In particular,
+.PP
+ host:user
+.PP
+is converted to
+.PP
+ user@host
+.PP
+to be consistent with the
+.IR rcp (1C)
+command.
+.PP
+Also, the syntax:
+.PP
+ host!user
+.PP
+is converted to:
+.PP
+ user@host.UUCP
+.PP
+This is normally converted back to the
+``host!user''
+form
+before being sent on for compatibility with older UUCP hosts.
+.PP
+The current implementation is not able to route messages
+automatically through the UUCP network.
+This feature is planned for the 4.2 release.
+Until that time you must explicitly tell the mail system
+which hosts to send your message through
+to get to your final destination.
+.PP
+.I Case Distinctions.
+Domain names (i.e., anything after the ``@'' sign)
+may be given in any mixture of upper and lower case
+with the exception of UUCP hostnames.
+Most hosts accept any mixture of case in user names,
+with the notable exception of MULTICS sites.
+.PP
+.I Differences with ARPA Protocols.
+Although the UNIX addressing scheme
+is based on the ARPA mail addressing protocols,
+there are some significant differences.
+.PP
+At the time of this writing
+the only
+``top level''
+domain defined by ARPA is the
+``.ARPA''
+domain itself.
+This is further restricted to having only one level of host specifier.
+That is,
+the only addresses that ARPA accepts at this time must be in the format
+``user@host.ARPA''
+(where ``host'' is one word).
+In particular,
+addresses such as:
+.PP
+ eric@monet.Berkeley.ARPA
+.PP
+are not currently legal
+under the ARPA protocols.
+For this reason,
+these addresses are converted to a different format on output
+to the ARPANET,
+typically:
+.PP
+ eric%monet@Berkeley.ARPA
+.PP
+.I Route-addrs.
+Under some circumstances
+it may be necessary to route a message
+through several hosts
+to get it to the final destination.
+Normally this routing is done automatically,
+but sometimes it is desirable to route the message manually.
+An address that shows these relays are termed
+``route-addrs.''
+These use the syntax:
+.PP
+ <@hosta,@hostb:user@hostc>
+.PP
+This specifies that the message should be sent to hosta,
+from there to hostb,
+and finally to hostc.
+This path is forced
+even if there is a more efficient path
+to hostc.
+.PP
+Route-addrs
+occur frequently on return addresses,
+since these are generally augmented by the software
+at each host.
+It is generally possible to ignore all but the
+``user@host''
+part of the address to determine the actual sender.
+.PP
+.I Postmaster.
+Every site is required to have a user or user alias
+designated
+``postmaster''
+to which problems with the mail system may be addressed.
+.PP
+.I CSNET.
+Messages to CSNET sites can be sent to
+``user.host@UDel-Relay''.
+.SH BERKELEY
+The following comments apply only to the Berkeley environment.
+.PP
+.I Host Names.
+Many of the old familiar host names
+are being phased out.
+In particular,
+single character names as used in Berknet
+are incompatible with the larger world
+of which Berkeley is now a member.
+For this reason
+the following names
+are being obsoleted.
+You should notify any correspondents
+of your new address
+as soon as possible.
+.PP
+.ta 1i 1.2i 2.5i
+ OLD NEW
+ j ingvax ucbingres
+ p ucbcad
+ r arpavax ucbarpa
+ v csvax ucbernie
+ n ucbkim
+ y ucbcory
+.PP
+The old addresses will be rejected as unknown hosts
+sometime in the near future.
+.PP
+.I What's My Address?
+If you are on a local machine,
+say monet,
+your address is
+.PP
+ yourname@monet.Berkeley.ARPA
+.PP
+However, since most of the world does not have the new software
+in place yet,
+you will have to give correspondents slightly different addresses.
+From the ARPANET,
+your address would be:
+.PP
+ yourname%monet@Berkeley.ARPA
+.PP
+From UUCP, your address would be:
+.PP
+ ucbvax!monet.yourname
+.PP
+.I Computer Center.
+The Berkeley Computer Center
+is in a subdomain of Berkeley
+so that they may administer
+their own name space.
+Messages to the computer center
+should be addressed to one of:
+.PP
+ user@host.CC.Berkeley.ARPA
+.br
+ user%host.CC@Berkeley.ARPA
+.PP
+depending on where the message is being sent from.
+The
+``.Berkeley.ARPA''
+may be omitted if the message is sent from inside Berkeley.
+.PP
+For the time being
+Computer Center hosts
+are known within the Berkeley domain,
+i.e.,
+the
+``.CC''
+is optional.
+However,
+it is likely that this situation will change
+with time as both the Computer Science department
+and the Computer Center grow.
+.PP
+.I Bitnet.
+Hosts on bitnet may be accessed using:
+.PP
+ user@host.BITNET
+.PP
+This works from 4.2 machines.
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