See communications center.

See digest.

1. In e-mail, a specified portion of a message (e.g., the header, the body). [ANSDIT]
2. In cryptography, a predefined meaning or data representation within a message. [After X9.19]

Information outside of the message text, such as the header, trailer, etc. [INFOSEC-99]

A method of checking the accuracy of transmission of data by sending received data back to the sending end for comparison with the original data that have been stored there for this purpose. [From Weik '89]

A predetermined or prescribed spatial or time-sequential arrangement of the parts of a message that is recorded in or on a data storage medium.
Note: Messages prepared for electrical transmission are usually composed on a printed blank form with spaces for each part of the message and for administrative entries.

A frame that consists of the channel seizure signal, the mark signal, the message, the checksum word, and any possible filler marks. [T1.401-1998]

In the ITU-T X.400 Recommendations, the family of services and protocols that provides the functions for global electronic-mail (e-mail) transfer among local mail systems.

In radio communications, the message part or parts that (a) precede the text, i.e., the message body, in time or space according to established conventions and (b) may include several data items, such as address groups, routing indicators, action addressee designators, information addressee designators, exempted addressee designators, prosigns, prowords, clear indicators, date-time groups, originator designators, special instructions, and protocol symbols.… (Read More →)

[A] sequence of bits transmitted over a communications system for synchronizing crypto-equipment. Some off-line cryptosystems, such as the [. . . ] one-time pad systems, employ message indicators to establish decryption starting points. [INFOSEC-99]