REWRITE(6) REWRITE(6)
NAME
rewrite - mail rewrite rules
SYNOPSIS
/mail/lib/rewrite
DESCRIPTION
Mail(1) uses rewrite rules to convert mail destinations into
commands used to dispose of the mail. Each line of the file
is a rule. Blank lines and lines beginning with # are
ignored.
Each rewriting rule consists of (up to) 4 strings:
pattern A regular expression in the style of regexp(6). The
pattern is applied to mail destination addresses.
The pattern match is case-insensitive and must
match the entire address.
type The type of rule; see below.
arg1 An ed(1) style replacement string, with \n standing
for the text matched by the nth parenthesized sub-
pattern.
arg2 Another ed(1) style replacement string.
In each of these fields the substring \s is replaced by the
login id of the sender and the substring \l is replaced by
the name of the local machine.
When delivering a message, mail starts with the first rule
and continues down the list until a pattern matches the des-
tination address. It then performs one of the following
actions depending on the type of the rule:
>> Append the mail to the file indicated by expanding
arg1, provided that file appears to be a valid mail-
box.
| Pipe the mail through the command formed from con-
catenating the expanded arg1 and arg2.
alias Replace the address by the address(es) specified by
expanding arg1 and recur.
translate
Replace the address by the address(es) output by the
command formed by expanding arg1 and recur.
Mail expands the addresses recursively until each address
has matched a >> or | rule or until the recursion depth
indicates a rewriting loop (currently 32).
If mail(1) is called with more than one address and several
addresses match | rules and result in the same expanded
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arg1, the message is delivered to all those addresses by a
single command, composed by concatenating the common
expanded arg1 and each expanded arg2. This mail bundling is
performed to reduce the number of times the same message is
transmitted across a network. For example, with the follow-
ing rewrite rule
([^!]*.bell-labs.com)!(.*) | "/mail/lib/qmail '\s' 'net!\1'" "'\2'"
if user presotto runs the command
% mail plan9.bell-labs.com!ken plan9.bell-labs.com!rob
there will follow only one execution of the command
/mail/lib/qmail presotto net!plan9.bell-labs.com ken rob
Here /mail/lib/qmail is an rc(1) script used for locally
queuing remote mail.
In the event of an error, the disposition of the mail
depends on the name of the command executing the rewrite.
If the command is called mail and is run by $user, the com-
mand will print an error and deposit the message in
/mail/box/$user/dead.letter. If the command is called
rmail, usually because it was invoked to deliver mail arriv-
ing over the network, the message will be returned to the
sender. The returned message will appear to have been sent
by user postmaster.
SEE ALSO
mail(1)
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