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From: rickert@mp.cs.niu.edu (Neil Rickert)
Newsgroups: comp.mail.sendmail
Subject: Re: Rewrite rules return null
Message-ID: <1991Apr23.174957.21196@mp.cs.niu.edu>
Date: 23 Apr 91 17:49:57 GMT
References: <78@motto.UUCP>
Distribution: na
Organization: Northern Illinois University
Lines: 34

In article <78@motto.UUCP> murray@motto.UUCP (Murray S. Kucherawy) writes:
>What does it mean when a rewrite rule returns nothing?  Will it produce
>an error in actual use, or will sendmail timeout, or will it try again...
>what happens?

  What exactly do you mean by 'returns nothing'?

  If the rewrite ruleset does not return, you probably have in infinite loop
going which is burning up CPU cycles.  If it does return, it returns something,
possible the null string.

  It is permissible for a rewrite rule to return the null string.  You may
occasionally see SMTP mail where the envelope sender (the MAIL-From SMTP
command) lists a sender address of <> .  This is accomplished by returning
a null address from sender rewrite rule, as perhaps in:

R@		$@

 Something like this shows up in some versions of sendmail.cf, where an
incoming address <> is converted to just @, then later converted back if
the sending mailer uses SMTP.  However you should be very careful to never
output null addresses except for the SMTP envelope sender.  Just imagine
what will happen to the Unix 'From ' line on say UUCP mail, if you did that
there.

 Many rulesets prefer to replace null addresses with either Postmaster or
with MAILER-DAEMON.


-- 
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  Neil W. Rickert, Computer Science               <rickert@cs.niu.edu>
  Northern Illinois Univ.
  DeKalb, IL 60115                                   +1-815-753-6940