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SpamAssassin is a spam filtering program that runs on our mail server. It analyzes the content of incoming messages, and assigns points based on a variety of tests. If enough points are accumulated, the message is considered spam, and can then be deleted, or have the subject header changed to allow for easy filtering with your email software. In our experience, SpamAssassin will correctly identify over 70% of all incoming spam, with very few false positives.

SpamAssassin can be customized for each mailbox through our webmail interface. Here’s how:

General Settings

The Spam Score adjusts the sensitivity of the spam filter. The lower the number, the more likely a message will be considered spam. If you find you are getting a lot of spam that isn’t being caught, you can lower this number, but be advised that by doing so you increase the likelihood that legitimate email will be tagged as spam.

If you want to disable SpamAssassin altogether, set the Spam Score to 999.

Rewrite Subject Line. This string will be appended to the beginning of any message considered spam. The default string is “!!SP”… You can change this string, or remove it altogether. You can still identify spam messages by using the “X-Spam-Status” header. (it will contain the word “Yes”)

Most email client software will allow you to setup a mail rule to automatically filter any message with “!!SP” in the subject line into a Junk mail folder, allowing you to monitor messages being tagged as spam to insure legitimate email isn’t being tagged.

Personal Allow/Deny Address List

This is where you can Whitelist (allow) or Blacklist (deny) email from specific addresses. If you find that an email from a mailing list (for example) is being tagged as spam, you can Whitelist the email address that is sending the email. Just type in the address in the Address bar, select “Whitelist from” from the pulldown menu and click “Add New Address”. You will see the new address in the list above.

Note that you can also add addresses to the Allow or Deny list right from an email from inside webmail. If you open a message in webmail, you will see in the header a link to Allow Sender, Allow Domain, Block Sender and Block Domain. By clicking one of these links, the sender will be added to your personal allow/deny list. Be aware, however, that blocking the address from a spam message will probably not do anything, as most spam comes from forged addresses.

Add New Score

SpamAssassin allows you to change the default score applied to one of the many tests that are run on incoming email. This is not something that LMi.net is in a position to provide technical support for, but you are welcome to give it a try at your own risk.

To find out which rules would be best to modify, you’ll need to have handy some spam that was not caught by Spamassassin. First, look at the full headers of the uncaught spam. If the message was sent through Spamassassin (messages over a certain size are not send through the filters, as they bog down the server), you will see X-Spam headers, like so:

X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on spamdd.lmi.net
X-Spam-Level: *
X-Spam-Status: No, score=1.1 required=5.0 tests=HTML_MESSAGE,MIME_QP_LONG_LINE,
	T_DKIM_INVALID,URIBL_GREY autolearn=disabled version=3.3.1

The important header is the X-Spam-Status header. There you can see which tests came back positive, along with what the total score was. You can look up the rules at http://spamassassin.apache.org/tests_3_3_x.html (though those rules are maintained by the people who run Spamassassin and are, unfortunately not complete, or even always accurate). You can then modify the score for one or more of those rules via the “Add New Score” box in your Spam settings. This is dangerous and can result in regular email being marked as spam, so it’s important to watch for false positives after doing this.