Exchange 2003 / Outlook 2003, one user intermittently sends duplicate emails...

I have a Exchange 2003 SP2 / Outlook 2003 SP3 / Windows XP SP2 environment. I have 40 users... ONE of my users sends a duplicate email every 4th or 5th email they send out. The receiver (internal or external) will see two of the exact same messages. However, when tracking the message in Exchange 2003 you can see that the messages in fact have different message ID's and Exchange thinks two were sent. So it appears it's not a exchange issue but an outlook issue??? Hard to say.

A few notes:
Is it virus scan? - No, this happens with the scanner on or off
New software installed on the users pc? - No, machines are locked down and nothing has been installed. Full adware and spyware check were run.
SMTP issue? - No, no one else is sending duplicates
Latest updates installed? - Yes, all updates for windows xp, exchange 2003, and outlook 2003 have been installed
Sync issue? - Doesn't appear to be, user is local with one copy of there mailbox open only... They are using cached mode with no sync errors.
POP / IMAP issue? - No, my server does not allow either.
Blackberry issue? - If it is, don't know how it's possible. We do have a blackberry server, but the messages are not being sent from the handheld, they are being sent directly from the users laptop.

Who is Participating?
markahaysConnect With a Mentor Commented:
I ran into the same problem with users running Outlook 2007, 2003 and Express on XP.  The issue seems to be linked to the "server timeout" value on the sender's copy of Outlook -- and a bug in the Outlook resend function.  Anything that delays the send process can trip the limit, e.g. emails that have large file attachments, a slow wireless connection, slow email server response, and delays caused by antivirus scans.  This can occur whether the user is linked to an Exchange server, Unix email server or simply connecting to the Web to via an ISP.  

If the timout is tripped, Outlook continues to 'retry' -- even though the message was already sent.  In one case, an employee sent an email with a 4Mb file attachment -- and the recipient received 42 copies before his mailbox filled up!  (Which caused yet-more problems...)

The best solution appears to be to increase the server timeout value in Outlook -- to 5+ minutes if you have a fast connection, or more if the connection and throughput are slower.   (Select the main email account and pick edit/change, then "More Settings" then the "Advanced" tab.)

I hope this is helpful!
BigZWillisAuthor Commented:
One more note:

- The duplicate item does NOT show up in the users sent items (just the original does)
See this..
To delete mails use this.
You may want to look at some of the utilities here: to remove duplicate messages, but keep one of each unique message.
Make sure to remove all rules firstly in many case that's the issue.
BigZWillis, I have the exact same issues and was wondering if you ever reached a resolution or at least narrowed down the cause.  My configs are identical to yours, however i'm also running Antigen 9.0 For MS Exchange Server 2003, which i've read can cause issues with SMTP.

Any help would be appreicated!

Thanks in advance!
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