The problem that you are experiencing is not unique. There have been many reports of this with both Exchange 2000 and Exchange 2003. However, without knowing the details of your configuration, it's not possible to pinpoint the cause. For example, in some cases the problem may be tied to POP3 delivery, while in others it is tied to delays caused by virus scanners. Here are two steps to start the troubleshooting process:
- Disable any archival features on the server.
- Disable antivirus scanning both on the server and on the workstation. (This step should only be temporary as a test. Do not disable it permanently.)
We've seen the multiple email issue with TLS encryption. If you use TLS encryption, the Internet email session takes a while to encrypt the message when sending, especially with larger attachments. If the email session doesn't end properly during the encryption phase, then the email message is requeued for sending on the sender's Internet email server. Basically, the TLS session times out, however the recipient still gets the original email. Later, the requeued message tries again. You basically get the message multiple times.
You might be able to tweak the timeout settings in TLS to help correct this problem. Not everyone uses TLS encryption, so this would only happen when TLS is required between the sender and the receiving server.
This answer does not include another cause of multiple copies of the same email being sent to the same email address – the email may be stuck in Exchange's temporary table.
We had a similar issue with an email being sent every night at midnight, but after deleting our Exchange temporary table with MFCMAPI, the issue went away.
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Dig Deeper on Legacy Exchange Server versions
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