SUMMARY - Repeating emails

I got A LOT of responses.  Most people wanted the answer as soon as I got it, 
but I did get some suggestions.  Some people suggested using other mail programs 
such as qmail or postfix or notes.  A few pointed at the firewall, but that's 
not the case.  One reply (no name, just "sysadmin@<domain>") suggested using 
procmail, but asked why I don't just send SUCCESS.  The answer is that the 
remote server doesn't hear it or doesn't listen and resends the message.  I 
think that there's a mail lock problem on the remote, and that the queue is read 
too frequently.  It's not sendmail per se, but if it were, it would probably 
have been started like this:

	/usr/lib/sendmail -bd -q5s

If you DID start sendmail like that, the known-to-work file locks would prevent 
concurrent children from delivering the same queue entry simultaneously.  And 
people think I should get rid of it?  Why??

I did get suggestions to check that /var/mail/${USER} is set to mail and not the 
users' group.  There are a few "wrong" groups, but those users never have this 
problem.  The other suggestion was to check the delivery flags on Mlocal and 
remove the "m".  Thanks to Brad Parks for both of those, but I'm way ahead of 
you on Mlocal.  I didn't know about the group thing, but it's not that.

We've narrowed it down to THREE conditions that cause the same message to be 
received as many as 400 times from a remote server:

  1 -	Mailing List program went crazy and sent multiple copies.  This usually 
results in the user receiving only ten or twenty copies.  Remote domain admin 
will flip the switch and stop it from happening as he/she apologizes.
  
  2 -	The message comes from a particular domain who shall remain nameless 
because it seems they don't know what they're doing.  I found out by looking at 
the logs that about a third of all messages from this domain are resent at least 
two times (total 3 messages) and that at least one per week is resent not less 
than 100 times.  Remote domain has no admin, only an "abuse" address, and will 
send a form letter stating that the apparently offending address is not valid 
and is being forged.  Then they give us an URL on how to prevent spam.
  
  3 -	MIME content length is wrong.  The spool runs out so the delivery MTA 
keeps sending the message until the length is correct (never) or until the max 
time is spent on the queue (5 days) or until I tript REJECT and start getting 
complaints from all the bounces.  Remote admin will usually remove the queue and 
everything will be fine.  We both apologize ;)

Conclusion:  SendMail, while many of you may think is klunky and unmanageable, 
is NOT the problem here.  The problem is the way a certain NON-RFC-compliant 
mail server does not listen when an RFC-compliant server talks.

Solution:  So long as bad delivery agents are allowed to exist, there appears to 
be no real solution.  However, as soon as I find the answer I will post it to 
the list.


Happy Holidays to all.



    Snippit from original message:
    
    Does anyone know if it is possible to configure SendMail to check the
    headers for the Message-Id:  line and refuse it if it has already been
    delivered?  That would seem the most logical thing to do.  If this is not
    possible, then could it somehow be otherwise configured to recognize a
    message has been received more than once and give the remote server the
    "Enough Already!"  signal?
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