SMTP Spam Filter

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SMTP Spam Filter, also known as "SpamCatcher", is a service for customers who run their own mail servers, but don't have either the ability or resources to install and maintain their own copy of SpamAssassin.

Since XMission has an extremely well maintained spam filter, we have figured out a way to “apply” our filters to these customers' external mail servers.

Sales Information

You can read more of the general details on the SpamCatcher service and what it provides on our product page:

Please contact our Sales team with any questions about the product. Sales contact information.


Please contact your Sales rep for pricing. Some XMission accounts qualify for free or discounted SMTP Filtering.

Setup and Functionality

Please note: You must first activate the SMTP Spam Filter service with XMission _before_ you apply these settings to avoid missing any email.

To set up SMTP Spam Filtering, the customer needs to point their domain's MX record to “” and provide XMission with the Static IP address of their mail server. Once this information has been updated in the XMission mail servers and the customer's DNS, it will begin working (total time is approximately 15 min).

It works by making XMission's incoming mail servers the customer's incoming mail servers. With their domain's MX record pointed to us, we receive their mail. Our incoming servers apply the spam filtering by using the same RBLs (Real-time Blackhole List), virus scanning, and spam scoring that they do for any other XMission email.

Once the message has been processed and received, it is relayed to, XMission's email queuing server. Etrn, in turn, relays the message to our customer's mail server at the IP address they have provided.

Optionally, XMission can also configure our system to delete mail at a particular score on the customer's behalf, though typically the customer will use the provided SpamAssassin headers to filter mail as they see fit. Any mail scoring 25 or higher is rejected by default. To set a custom discard score, please contact XMission support or your Sales agent.

In addition to the filtering, this setup provides the customer with the ability to change their mail server without having to deal with DNS updates, and keeps the customer's mail server “hidden” from the world. They will only see SMTP conversations from XMission's network, and can apply appropriate firewall rules. Finally, if their server goes down, XMission will queue the customer's mail for up to one week.

If a customer's mail gets queued, they can point their mail servers to to send the ESMTP ETRN command. When their mail server issues that command, etrn will flush mail for their domain to the IP address provided to XMission.