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List:       qmail
Subject:    Re: Duplicate mails
From:       John Johnstone <jjohnstone () tridentusa ! com>
Date:       2008-03-31 20:35:04
Message-ID: 47F14AF8.4090501 () tridentusa ! com
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Krish wrote:
> Dear all,
> 
> Whenever any of our users send a huge mail around 9 MB
> the receiving end receives the mail over and over
> again around 15 times. Please let me know why this
> takes place. I have spamassassin and qmailscanner in
> effect. The mails are sent to multiple clients on
> different servers and they are all complaining about
> duplication. My timeoutconnect is 30 remote is 300 and
> smtpd is 300.  I sent a huge mail to a test account on
> another server and I received the mail however inmy
> sending server I see the message still in the queue. 
> 
> Please let me know steps to check and rectify this
> problem.
> 
> thank u 

When a large message is transferred in a SMTP transaction, if the 
transaction takes too long to complete, the sender times out and thinks 
the transaction has failed.  If the receiving system takes too long to 
acknowledge the receipt of a message, the sender thinks that the message 
wasn't sent successfully even though eventually the receiver does 
complete the transaction and does finish receiving the message.  Later 
on, the sender will then retry sending the message and the whole process 
repeats.  This cause multiple copies of the message to be received by 
the recipient.  This can be fixed by increasing the timeout on the 
sending system.

If your users e-mail client is has a timeout value that is too short, it 
is the sending system that is causing the problem.  The default timeout 
for most mail clients is one minute which might not be long enough if 
your mail server takes too long to receive the message and send an 
acknowledgment back to the client.  If that's the case, your mail server 
has nothing to do with the problem and changing timeout values there 
will have no effect.

If you look at the Received headers of any of the problem messages and 
look at your smtpd and send logs you should be able to find out if the 
problem is happening between your clients and your server or between 
your server and the destination server.

-- 
John J.
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