Just as all addresses are first rewritten by rule set 3, so are all addresses rewritten last by rule set 4. Its job is to undo any special processing done by rule set 3, such as focusing. In this section we'll examine some typical rule set 4 rules.
# strip trailing dot off possibly canonical name R$* <@ $+. > $* $1 <@ $2 > $3
Note that this rule recursively removes as many trailing dots as it finds. Also note that the host part remains focused after rewriting.
Recall that rule set 3 converted the commas of source route addresses into colons (see Section 29.4.3, "Handling Routing Addresses"). Rule set 4 now needs to restore those commas:
R$* : $+ :$+ <@ $+> $1 , $2 : $3 <@ $4> <route-addr> canonical
This rule recursively changes all but one (the rightmost) colon back into a comma.
As a special note, under V8 sendmail, envelope-sender
route addresses are always surrounded by angle brackets
when passed to the delivery agent.
If this behavior is inappropriate for your site, beginning with
V8.7 it is possible to prevent this heuristic by specifying
F=d delivery agent flag (see Section 30.8.16).
Rule set 4 also removes angle brackets inserted by rule set 3 to focus on the host part of the address. This is necessary because mail will fail if they are left in place.
# externalize local domain info R$* <$+> $* $1 $2 $3 defocus
After defocusing, rule set 4 may need to convert some addresses
back to their original forms. For example, consider UUCP addresses.
They entered rule set 3 in the form host!host!user. Rule set
3 rewrote them in the more normal user@host form,
and added a
.uucp to the end of the host.
The following rule in rule set 4 converts such
normalized UUCP addresses back to their original form:
# UUCP must always be presented in old form R$+ @ $-.uucp $2 ! $1 u@h.UUCP => h!u