Mailing lists are a useful tool for commerce and recreation. They allow a user to send emails to a single address, and the email is then forwarded to all the members of the list in a broadcast fashion. Spammers used to send messages to a mailing list, and they would be forwarded to all the recipients. To prevent this, most mailing lists require users to authenticate themselves in some way. This is a manual process that deters spammers who rely on automated processing.

Often, mailing lists are archived on the Internet for reference. If a spammer's web spider reaches a mailing list archive, it will have access to the email addresses of all the people who have posted on the list. Consequently, the latest versions of all the popular mailing list management software disguise or munge email addresses when archiving them on the Web.

Some mailing lists are moderated, which means that submissions have to be approved by a moderator before they will be forwarded to list members...