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If a User is listed in multiple aliases or multiple mailing list or groups a message is sent to more than one of the aliases, mailing list or group the end User will receive multiple copies.

How to prevent to receive multiple copies to a user listed in multiple aliases or multiple mailing list or groups ?

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2 Answers 2

If a User is listed in multiple aliases or multiple mailing list or groups a message is sent to more than one of the aliases, mailing list or group the end User will receive multiple copies.

According to the Exim official guide, that's not true, unless the destinations resolve to pipes. Do you have an example?

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This de-duplication is true for any single messages that is being delivered to multiple addresses aliased to the same real (local) mailbox. The question was not clear whether this is the case, or if multiple, separate email are being sent with the same message ID, or if the message ID is different but the message body is identical. Google does seem to de-dupe those kinds of messages, and he's asking for the same in Exim I guess. –  Todd Lyons Jan 10 at 13:06

If the message arrives in a single transmission, then Exim should removed duplicates in the process of delivery. This is unlikely to happen if the domains are different, or have been forwarded. Check your logs for the offending messages.

If the messages arrive in separate deliveries with the same Message-Id it is fairly easy to remove duplicates using that header. Exim will deliver using procmail which can do the deduplication during delivery. During testing the duplicates can be delivered to a separate mailbox so nothing is lost.

I would encourage the user to unsubscribe from the duplicate addresses. A forward rule can be used to distribute to other addresses.

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