How can I stop Anti Spam services incorrectly blacklisting my mail server?

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Online Anti Spam services such as SpamCop have been known to blacklist a mail server if they receive a bounced message originally claiming to be from a user on their domain. Many system administrators later discover their mail servers has been blacklisted due to the following activity:

A spammer fakes a message to come from a SpamCop account. The spammer addresses this message to a user on your local server. Your server flags something in the message and consequently bounces this message back to the SMTP sender which in this example appears to be from a SpamCop server.


Under SpamCop’s own advice, you could implement a "sacrificial lamb" system. In clearer terms, configure a second mail server on your network to send out these potential message bounces.

You could configure the "Unknown User Action" in GMS to accept the message by sending it to your second server. The "Unknown User Action" on the second server would redirect to a local user account. This user account should be configured with an auto-responder.

As the second server isn’t responsible for delivering your company’s e-mail, it won’t matter as much that this server has been blacklisted. It has therefore served its purpose as a " sacrificial lamb" server.

Another example, again using a second physical machine, would be to employ a gateway server sitting in front of the internal mail server. It is common to find a gateway server acting as the primary layer of boundary protection to the internal server, often offering Anti Spam and/or Anti Virus functionality.

The role of the gateway will mean that it will bounce mail for unknown users and continue to send locally addressed e-mail to the internal server. This means that if the gateway gets blacklisted it won’t effect the sending out of external mail as this is the job of the internal server.

See Also:

Keywords:generate bounce unknown spamcop gateway boundary protection sacrificial lamb

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