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Outlook cant fetch mail from my qmail server, but testing it via telnet works fine

Jun 17th, 2004 12:05
Joseph Sullivan, Jonathan de Boyne Pollard, Stein Robert Roessaak, http://www.clansullivan.com/joseph/


There is a well-known problem with Microsoft Outlook Express, 
whereby it fails to cope with messages that contain certain 
patterns of data (in particular, lone carriage returns at the 
ends of physical header lines).  The error message that it 
displays ("Your server has unexpectedly terminated the 
connection.") tries to place the blame on the POP3 server, but 
this is a Microsoft Outlook Express bug.  
It isn't anything to do with "qmail" at all.  "qmail" has a 
deliberately transparent design.  What comes out at the POP3 
end is exactly what went in at the SMTP Relay end.  The problem 
here is that one MUA, at the sending end (and possibly in 
combination with the MTS at the sending end), has generated a 
message that causes problems for another MUA, Microsoft Outlook 
Express, at the receiving end.  This is a compatibility problem 
between two MUAs, and nothing to do with "qmail".
You might think that MUAs shouldn't be creating such messages 
(because they violate a requirement in section 2.3 of RFC 
2822).  In which case, you should complain to the author of the 
generating MUA at the sending end, whatever that is, and have 
that MUA fixed.
You might, on the other hand, think that recipient MUAs should 
be robust, and not vulnerable to any unusual message contents.  
("Do not trust data received from the network.", and all that.)  
In which case, you should complain to the author of Microsoft 
Outlook Express.
You might foolishly decide not to complain to Microsoft and sit 
around asserting that "'qmail' should do something", justifying 
this erroneous concept of how to fix a Microsoft Outlook 
Express problem by stating that Microsoft doesn't fix such 
things.  However, this justification is patently false.  In 
2003, Microsoft issued several critical updates that fixed 
vulnerabilities in its MUA softwares that were due to them not 
being able to safely and robustly handle certain patterns of 
message content.
-- Update: A patch for qmail is available at 
http://www.clansullivan.com/joseph/ that partially fixes this problem.  
while I may repeat that qmail is NOT causing the problem, many admins 
nevertheless find themselves in a position of having to do something 
about it.  If this is you, grab the patch and apply it to qmail 1.03.  
The patch will cause Qmail to reject with an error messages containing 
an illegal (see RFC) 0D0D sequence.