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MAC

Moves, Adds and Changes

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Mailbox

A reference to the location where voicemail messages for a particular user are stored.

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MAPI

Messaging Application Program Interface

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Mb

Megabyte - 
A measure of computer processor storage and real and virtual memory, a megabyte (abbreviated Mb) is 2 to the 20th power bytes, or 1,048,576 bytes in decimal notation.

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MPD


Meter Pulse Detection
 - A BT service for their analogue lines, to allow a subscriber to accurately establish the charge of a telephone call. To a subscriber, it was a Meter Pulse received by monitoring equipment down their telephone line. To BT, it was a Charge Unit recorded on the subscriber's meter in the local BT exchange. During a call, the first pulse would be transmitted the moment the call connected. Subsequent pulses would be transmitted at time intervals thereafter, the interval depending upon the telephone number dialled and the time of day.

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Modem

Modulator-De Modulator