An Ounce of Prevention. . .

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Before we look at ways to "cure" the junk mail problem, we should remember that preventing junk mailers from harvesting e-mail addresses is the most effective, reliable, and efficient method for avoiding unwanted messages. If they don't have your address, they can't send you mail.

You should think twice before doing any of the following:

• Sending anyone a message (which contains your address in the From header field or envelope return path)

• Posting a message to a Usenet newsgroup (From field, again)

• Filling out a Web form that asks for your e-mail address

• Including your e-mail address on a Web page or business card

• Giving your address to a friend or relative

Do you really trust the recipient(s) not to sell your address to marketers or disclose it to others, even accidentally? In the case of a public forum such as a mailing list or newsgroup, there could be thousands of recipients. Expecting an address published publicly to remain private is naïve. Even a well-meaning friend or relative can hand your address to a junk mailer without realizing it, for example, by sending you a Web greeting card through an unscrupulous Web site.

Remember that once an address has been publicly disclosed, there's no way to prevent junk mailers from using it. At that point, your choice is whether to implement spam controls or abandon the address. As you'll see, spam controls are time consuming and often unreliable or ineffective. Abandoning the address means you'll have to get a new one and distribute it to everyone who should have it—usually a difficult task.

qmail's extension addresses provide a handy way to track and control your e-mail address. Chapter 4, "Using qmail," shows how you can turn a single address into an unlimited set of addresses that can identify their source and be revoked by the user in the event that they fall into the wrong hands.

For example, if your main address is [e-mail], you could register at Example's Web site with [e-mail]. If Example then sells that address to a mass marketer, and you want to disable the address, you could create a $HOME/.qmail-web-example:com file containing this:

 |bouncesaying "This address has been disabled." 

which would disable the bfie-web-example.com address and cause senders to receive a bounce message. If you want to throw those messages away, because junk mail usually has an invalid return address, you could create a non-empty $HOME/.qmail-example:com with no delivery instructions:

 # don't deliver or bounce mail to [e-mail] 

Note 

An empty dot-qmail file is treated the same as one that contains the defaultdelivery instructions, so to throw messages away undelivered, the dot-qmail file must be non-empty but must also contain no delivery instructions. In other words, it must contain only comments—lines starting with # characters.

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