SMTP Spam Filter

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Revision as of 07:31, 6 August 2014 by Ehigbee (talk | contribs) (Configuring SpamCatcher)
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All mail servers require an SMTP feed to send and receive email.

Our SMTP Spam Filter and mail feed, which we call "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.

XMission uses a combination of internal and external RBLs (IP and URI), a cluster of SpamAssassin servers running a large custom ruleset, and the ClamAV virus scanner to keep our customers safe. SpamCatcher “applies” these filters and processes to a customer's external mail server environment.

By including mail spooling, SpamCatcher also protects customers in the case of an unexpected outage. XMission will queue customer mail for up to 8 days.

Pre-emptive Blocking And How XMission Filtering Works

By default, any mail with a score of 25 or higher is rejected and thus not delivered to the customer mail server saving bandwidth and mail server load.

SpamCatcher can be configured to delete mail at a particular score on the customer's behalf. To set a custom discard score, please contact XMission support.

For a deeper understanding of how XMission's spam and virus filtering works, please reference this blog article:

Easy DNS Handling

In addition to the filtering, this service provides customers 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. Customer mail servers will only see SMTP conversations from XMission's network, and can apply appropriate firewall rules.

Configuring SpamCatcher

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

To set up SMTP Spam Filtering, customers need 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 the domain's MX record pointed to XMission, we receive the mail and 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 thousands of other XMission customer email addresses.

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

Mail Queuing And Message Retrieval

SpamCatcher queues all customer email for up to 8 days in the case of an outage.

Retrieving queued mail is easy. From the customer mail server, point to and send the "ESMTP ETRN" command. When the command is received from a verified mail server, all queued mail will be delivered for their domain.

Sales Information

SpamCatcher product page:

Please contact your Sales agent with any questions or to order the service. Sales contact information. Some XMission accounts qualify for free or discounted SMTP Filtering.

XMission can help with domain name registration and help keep your mail transactions secure with SSL certificate registration services

If you have any questions about this service please contact your XMission agent.