+.sh 4 "Semantics of rewriting rule sets"
+.pp
+There are five rewriting sets
+that have specific semantics.
+These are related as depicted by figure 2.
+.(z
+.hl
+.ie n \{\
+.(c
+ +---+
+ -->| 0 |-->resolved address
+ / +---+
+ / +---+ +---+
+ / ---->| 1 |-->| S |--
+ +---+ / +---+ / +---+ +---+ \e +---+
+addr-->| 3 |-->| D |-- --->| 4 |-->msg
+ +---+ +---+ \e +---+ +---+ / +---+
+ --->| 2 |-->| R |--
+ +---+ +---+
+.)c
+
+.\}
+.el .ie !"\*(.T"" \
+\{\
+.PS
+boxwid = 0.3i
+boxht = 0.3i
+movewid = 0.3i
+moveht = 0.3i
+linewid = 0.3i
+lineht = 0.3i
+
+ box invis "addr"; arrow
+Box3: box "3"
+A1: arrow
+BoxD: box "D"; line; L1: Here
+C: [
+ C1: arrow; box "1"; arrow; box "S"; line; E1: Here
+ move to C1 down 0.5; right
+ C2: arrow; box "2"; arrow; box "R"; line; E2: Here
+ ] with .w at L1 + (0.5, 0)
+ move to C.e right 0.5
+L4: arrow; box "4"; arrow; box invis "msg"
+ line from L1 to C.C1
+ line from L1 to C.C2
+ line from C.E1 to L4
+ line from C.E2 to L4
+ move to BoxD.n up 0.6; right
+Box0: arrow; box "0"
+ arrow; box invis "resolved address" width 1.3
+ line from 1/3 of the way between A1 and BoxD.w to Box0
+.PE
+.\}
+.el .sp 2i
+.ce
+Figure 2 \*- Rewriting set semantics
+.(c
+D \*- sender domain addition
+S \*- mailer-specific sender rewriting
+R \*- mailer-specific recipient rewriting
+.)c
+.hl
+.)z
+.pp
+Ruleset three
+should turn the address into
+.q "canonical form."
+This form should have the basic syntax:
+.(b
+local-part@host-domain-spec
+.)b
+If no
+.q @
+sign is specified,
+then the
+host-domain-spec
+.i may
+be appended from the
+sender address
+(if the
+.b C
+flag is set in the mailer definition
+corresponding to the
+.i sending
+mailer).
+Ruleset three
+is applied by
+.i sendmail
+before doing anything with any address.
+.pp
+Ruleset zero
+is applied after ruleset three
+to addresses that are going to actually specify recipients.
+It must resolve to a
+.i "{mailer, host, user}"
+triple.
+The
+.i mailer
+must be defined in the mailer definitions
+from the configuration file.
+The
+.i host
+is defined into the
+.b $h
+macro
+for use in the argv expansion of the specified mailer.
+.pp
+Rulesets one and two
+are applied to all sender and recipient addresses respectively.
+They are applied before any specification
+in the mailer definition.
+They must never resolve.
+.pp
+Ruleset four is applied to all addresses
+in the message.
+It is typically used
+to translate internal to external form.
+.sh 4 "IPC mailers"
+.pp
+Some special processing occurs
+if the ruleset zero resolves to an IPC mailer
+(that is, a mailer that has
+.q [IPC]
+listed as the Path in the
+.b M
+configuration line.
+The host name passed after
+.q $@
+has MX expansion performed;
+this looks the name up in DNS to find alternate delivery sites.
+.pp
+The host name can also be provided as a dotted quad in square brackets;
+for example:
+.(b
+[128.32.149.78]
+.)b
+This causes direct conversion of the numeric value
+to a TCP/IP host address.
+.pp
+The host name passed in after the
+.q $@
+may also be a colon-separated list of hosts.
+Each is separately MX expanded and the results are concatenated
+to make (essentially) one long MX list.
+The intent here is to create
+.q fake
+MX records that are not published in DNS
+for private internal networks.
+.pp
+As a final special case, the host name can be passed in
+as a text string
+in square brackets:
+.(b
+[ucbvax.berkeley.edu]
+.)b
+This form avoids the MX mapping.
+.b N.B.:
+This is intended only for situations where you have a network firewall,
+so that your MX record points to a gateway machine;
+this machine could then do direct delivery to machines
+within your local domain.
+Use of this feature directly violates RFC 1123 section 5.3.5:
+it should not be used lightly.
+.sh 3 "D \*- define macro"
projects / unix-history / blobdiff