The Non-confirming Mailing List (NML) is a database of IP addresses that have been demonstrated to be the sources of mailing lists, which do not fully verify the email addresses on their list. This means that they do not confirm that the owner of the email address that is placed on their mailing list has, in fact, granted their permission to be included on the mailing list.

An IP address which is found to be involved with sending mail to a mailing list that does not fully verify addresses prior to their addition to the mailing list, or sending mail to those unconfirmed email addresses, will be considered for inclusion in the MAPS NML. After a mailing list has implemented a procedure to ensure that the owner of each email address has fully confirmed their permission to have their address added to the mailing list, a listed IP address can be removed from the MAPS NML.