Chapter 8: Controlling Junk Mail

---

Highlights

Junk mail—Unsolicited bulk e-mail (UBE), Unsolicited Commercial E-mail (UCE), or spam—is the bane of the e-mail user. Unscrupulous marketers harvest e-mail addresses from every available source including Web sites, Usenet newsgroups, and chat forums. They then send large numbers of messages to these addresses enticing the recipients to buy their new miracle product, get rich quick using their unique and perfectly legal scheme, access the hottest pornography, join the one true faith, or—well, the list is endless.

The methods employed by mail administrators and users to control spam are as varied as the spammers' pitches. Many spam controls are heuristic, and as more users adopt them and block more unsolicited mail, the spammers adapt and find a way around the blocks. The process has been likened to an arms race, with both sides developing more sophisticated methods to counteract their opponents.

Spam controls can be employed on two levels: to all mail entering the system (by the system or mail administrator) or to mail for only one user or address (by the user). Additionally, controls can be advisory, identifying a message as potential junk mail, or mandatory, blocking the delivery of mail identified as unwanted. A further qualification of spam controls is that they can be proactive, blocking junk mail before it is received, or reactive, disposing of it after it's been received but before it's been delivered.

Caution 

Although junk mail is immediately obvious to the user, automatic controls cannot always distinguish spam from legitimate mail. Therefore, mandatory spam controls also block some legitimate messages. Users should be notified when mandatory spam controls are in use, and, preferably, should be given the option not to use them.

Chris Hardie maintains the qmail Anti-Spam HOWTO (http://www.summersault.com/chris/techno/qmail/qmail-antispam.html), a good resource for users and administrators dealing with unwanted mail on qmail systems.

---