Machine cancellation - The obliteration of postage stamps by mechanical means.

Mailbag - The bag in which mail is transported by a mailman, train, or some other means of conveyance.

Mailbox - The container used to collect mail. Also known as 'pillar box' or 'collection boxes' (where people can deposit their mail for later pickup). Mailboxes are also used at households and businesses to receive mail.

Margin - The unprinted area around the edge of a postage stamp or stamp sheet; in the case of an imperforate stamp, the width, number and regularity of the margins strongly affects the value, the ideal being a wide, even margin along each side.

Maximum card - A picture postcard bearing a postage stamp and a postmark relevant to the picture on the card. The design on the stamp usually mirrors that on the postcard. The postage stamp is usually affixed to the picture side to heighten the effect. This style of use was begun in Europe at the beginning of the twentieth century and remains popular.

Metered mail - Mail whose postage is paid by a machine that tracks the amount of postage applied by the machines.

Miniature sheet - Small souvenir sheet of stamps bearing in the centre a small number (typically one or four) of a feature or charity stamp, often with imprint and other details in the wide margins; perf. or imperf. Often produced solely for collectors, though valid for postage.

Missent - A letter missent (usually through an illegible address) to the wrong town, applied to indicate the reason for delay in delivery.

Mixed franking - A cover franked with adhesives of two different issues (but usually applied to two different reigns or two different currencies).

Money Order - An order for the payment of a specified amount of money, usually issued and payable at a bank or post office.

Mute Cancellations - (Dumb cancellation) - An obliteration handstamp containing neither figure nor letter, often made of cork. Used for a variety of purposes including: cancellation of postage stamps (Maltese cross); wartime security cancelling, and more.

Michel - The Michel catalog is the largest and best-known stamp catalog in the German-speaking world. First published in 1910, it has become an important reference work for philately