Bug in Exchange 2000/SMTP outgoing mail queue...

From: Søren Krøger (removethis-junk_at_kroger.dk)
Date: 02/22/05 

Date: Tue, 22 Feb 2005 10:44:03 +0100

Hi

It seems like the queue handling in Exchange2000/SMTP has a little bug
causing Exchange to send duplicate mails.
I have observed this problem on a Windows2000/SP4 with Exchange2000/SP3.

It ocours when sending to multiple recipients and one
or more of the recipients are defered. It seems like exchange 2000
is sending to the whole list of recipient and then retries all
recipients except the first couple recipients which were accepted.

Example of a SMTP session from a exchange 2000 server:

The first time Exchange 2000 tries to deliver the mail it looks like this:

helo domain.dk
250 mailserver.remotedomain.dk Hello [ipaddress]
mail from:<me@domain.dk>
250 OK
rcpt to:<rcpt1@remotedomain.dk>
250 Accepted
rcpt to:<rcpt2@remotedomain.dk>
452 Defered, please try again later
rcpt to:<rcpt3@remotedomain.dk>
250 Accepted
rcpt to:<rcpt4@remotedomain.dk>
250 Accepted
rcpt to:<rcpt5@remotedomain.dk>
452 Defered, above quota or something
rcpt to:<rcpt6@remotedomain.dk>
250 Accepted
data
354 Enter message, ending with "."
bla bla bla text
.
250 OK id=messageid

..... now the exchange server is trying to send the same message again:

helo domain.dk
250 mailserver.remotedomain.dk Hello [ipaddress]
mail from:<me@domain.dk>
250 OK
rcpt to:<rcpt2@remotedomain.dk>
250 Accepted
rcpt to:<rcpt3@remotedomain.dk>
250 Accepted
rcpt to:<rcpt4@remotedomain.dk>
250 Accepted
rcpt to:<rcpt5@remotedomain.dk>
452 Defered, still above quota or something else...
rcpt to:<rcpt6@remotedomain.dk>
250 Accepted
data
354 Enter message, ending with "."
bla bla bla text
.
250 OK id=messageid

... now the third time, exchange retries to deliver the message....

helo domain.dk
250 mailserver.remotedomain.dk Hello [ipaddress]
mail from:<me@domain.dk>
250 OK
rcpt to:<rcpt5@remotedomain.dk>
250 Accepted
rcpt to:<rcpt6@remotedomain.dk>
250 Accepted
data
354 Enter message, ending with "."
bla bla bla text
.
250 OK id=messageid

... and now the message is delivered and removed from the exchange 2000
queue.

As you can see, the message is delivered
1 time to rcpt1, rcpt2 and rcpt5
2 times to rcpt3 and rcpt4
3 times to rcpt6

This means that Exchange 2000 is not sorting out the accepted rcpt's
correctly.
The correct behaviour with this example would be:
1. try with all addresses
2. try with rcpt2 and rcpt5
3. try with rcpt5

Does somebody know a fix for this issue?
I have searched Microsofts homepage all day, without success...

Thanks in advance.

Best regards

Søren

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