i/s Back Issues

Volume 18

No. 3  January/February 2003

SpamAssassin Takes a Swipe at Junk Email

Jonathan Hunt

What can you do about spam, that unsolicited, unwanted junk email that keeps appearing in your inbox? Up until now your options have been limited. You could try to filter key phrases like "toner cartridge." You could buy software that claims to prevent spam, but only works a little. Or you could live with the most common solution, just deleting spam and moving on. As the volume of spam has increased, so has the frustration and the time lost dealing with it. IS has recently added some features to the MIT mail system to help you deal with spam.

SpamAssassin to the Rescue
IS is pleased to announce the installation of SpamAssassin on the MIT mail servers. The web site for this open source program is at http://spamassassin.org/

SpamAssassin performs a series of tests on email messages and issues a score based on how likely they are to be spam. The higher the score, the more likely that a message is spam. The score and a YES/NO flag are added to each message's header.

You may have noticed several new mail headers in your email relating to spam recently, specifically:

X-Spam-Flag: NO
X-Spam-Score: 4.5, Required 7.5

You can find more information on these and other new headers from the MIT Spam Screening web site at http://web.mit.edu/ist/help/nospam/

How Do You Filter Spam?
Your options depend on the email client you use. With POP clients, you can set up a filter so that messages with the X-Spam-Flag header set as YES are moved to another mailbox. With IMAP clients, you can configure your mailbox so that the server delivers all email flagged as spam to a sub-mailbox under your Inbox. You can further configure your spam settings so that email in that sub-mailbox is purged after some period of time. The default setting is to not purge the mailbox, so be careful about your quota: spam can use it up very quickly.

Separating spam from legitimate email is a difficult and ever-changing problem. The solution that MIT has implemented may not be sufficient in the future, so expect that the system will need to change over time. Also because spam filtering is hard, some legitimate messages will be scored as spam. IS recommends that if you choose to filter spam, you should scan through all the spam-flagged messages regularly for at least the first 6 to 8 weeks to be sure that any email you want does not end up lost with all the spam.

One of the most common message types that is incorrectly flagged as spam is subscription newsletters such as airline special fare emails and security announcements. To prevent these messages from being flagged as spam, you can customize your Allow list in your spam settings to not flag messages from a particular address as spam. You can also customize your personal spam threshold, the score above which messages are flagged as spam. All of your personal spam settings can be customized.

The Contents Are Untouched
Rest assured that the contents of your email are not being changed, filtered, or blocked. All email sent to you at MIT will be delivered to you. If you do nothing, the only change will be the added headers in your email. You must choose to make a filter in your email client or create a specific IMAP mailbox for any filtering to happen. If you choose the IMAP filter solution, you'll also need to choose to have that mailbox periodically purged of older messages or delete the messages yourself.

Information and Help
The MIT Spam Screening web site, mentioned earlier, is your best source of information on handling spam. It has

	A list of pros and cons about the POP and IMAP options
	Instructions on setting up the most common email clients to take advantage of spam scoring
	Details on customizing your personal spam settings

As of March 3, 2003, the Computing Help Desk will be available to help you implement the spam solution that is right for you. You can reach them at x3-1103 or <computing-help@mit.edu>.

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