enting opt-in mailing lists: many means of gathering user e-mail addresses remain susceptible to forgery. For instance, if a company puts up a Web form to allow users to subscribe to a mailing list about its products, a malicious person can enter other people's e-mail addresses — to harass them, or to make the company appear to be spamming. (To most anti-spammers, if the company sends e-mail to these forgery victims, it is spamming, albeit inadvertently.)
To prevent this abuse, MAPS and other anti-spam organizations encourage that all mailing lists use confirmed opt-in (also known as verified opt-in and (by spammers themselves) as double opt-in). That is, whenever an address is presented for subscription to the list, the list so
ftware should send a confirmation message to that address. The confirmation message contains no advertising content, so it is not construed to be spam itself — and the address is not added to the list unless the recipient responds to the confirmation message. See also the Spamhaus Mailing Lists vs. Spam Lists page. All modern mailing list management programs (such as GNU Mailman, Majordomo, and qmail's ezmlm) support confirmed opt-in by default.
