7. Managing obsolete email addresses
One of the problems with mailing lists is that they can quickly become obsolete as subscribers change their email address and do not remove old addresses from lists they are subscribed to. Ezmlm has a method to monitor bounced emails and can remove addresses from which emails regularly return.
Ezmlm uses the subscriber address and message number (encoded within the sender address) to track which message have bounced for which recipient. Since messages can bounce for a variety of reasons, ezmlm does not remove a subscriber from the list immediately. Instead it waits 12 days after the first bounce, then sends a warning message to the subscriber. The warning message lists the numbers of the messages missed. The user can retrieve these from the archive (if this feature has been enabled). If the warning message again bounces back, ezmlm waits another 12 days, then sends a probe message. If this probe message bounces the email address is removed from the subscriber database. This mechanism guarantees that a subscriber will not be removed due to a temporary error, while assuring that all non-existent or permanently failing addresses are removed.