Confirmed Opt-In

A new subscriber asks to be subscribed to the mailing list, but unlike unconfirmed opt-in, a confirmation e-mail is sent to verify it was really them. The person must not be added to the mailing list unless an explicit step is taken, such as clicking a special web link or sending back a reply e-mail. The web link or reply e-mail must contains some sort of secret word or token that can not be guessed by a malicious person. This ensures that no person can subscribe someone else out of malice or error. Mail system administrators and non-spam mailing list operators refer to this as confirmed subscription or closed-loop opt-in. Spammers sometimes call this method double opt-in, to imply that the confirmation is a duplication of effort and thereby to discourage its use. The use of this term is generally a good indicator that the marketer does not understand good mailing list practices and will do many other things wrong, such as reselling your e-mail address to others.