Mailbot: A piece of software that automatically replies to email.

Mail-merge: A process that enables the delivery of personalized messages to large numbers of recipients. This is usually achieved using email list management software working in conjunction with a database.

Merge-purge: The act of removing duplicate email addresses from a coalesced list that is composed of two or more existing lists.

MIME: Multi-Purpose Internet Mail Extensions – An extension of the original Internet email standard that allows users to exchange text, audio or visual files.

Moderated list: Moderators must approve any message posted to an email list before it is delivered to all subscribers. It is also possible for the moderator to edit or delete messages. A moderated list thus puts the list owner in the equivalent position as an editor of a newspaper.

Multipart/alternative: A message format that includes both text and HTML versions. Recipients can then open the message in their preferred format.

MX: Mail Exchanger - A mail exchanger record (MX record) is a type of resource record in the Domain Name System (DNS) that specifies a mail server responsible for accepting email messages on behalf of a recipient's domain, and a preference value used to prioritize mail delivery if multiple mail servers are available. The set of MX records of a domain name specifies how email should be routed with the Simple Mail Transfer Protocol (SMTP).