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I have installed Postfix with MailScanner on CentOS 5.4 as a smarthost for Exchange 2007. When a message gets quarantined and I later release it (, it gets delivered to the Exhcange box but does not appear in a user's mailbox.

Exchange message tracking log shows the message is marked as DUPLICATEDELIVER and therefore dropped.

How can I work around this situation? Maybe changing a message ID somehow while at the Postfix box or some other way?


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Duplicate detection is done by exchange based on 2 things, Message ID and Client Send time. I assume your quarantine here means that the suspicious message gets sent originally to the user, without the attachment, and then when cleared sent with it.

In this case the client send time and message ID are the same or both messages, hence the duplicated deliver pick-up, so you need to be changing either the message ID or the client send time to stop this occurring.

You can also disable Exchange duplicate delivery detection, or reduce the time that Exchange keeps a log of message details for checking for duplicates, but that could then increase the amount of real duplicate messages you receive.

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On the MailScanner side you can add 'Message-ID:' to the 'Remove These Headers' section of your MailScanner.conf file. The conf file actually states the following:

If you are having problems with duplicate message-id headers when you release spam from the quarantine and send it to an Exchange server, then add Message-Id.

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