If there is an external standard, the character set may already be defined. This indicates that the message is in no particular encoded format, but is to be presented to the user as is. Using the message encoding on returned mail makes it practical for a mail reading system to implement a reliable resending function, if the mailer generates it when returning contents. Message encoding is also used when mapping to X.400 to handle recursively included X.400 P2 messages. 4.3 Hex The encoding indicates that the body part contains binary data, encoded as 2 hexadecimal digits per byte, highest significant nibble first.
Lines consist of an even number of hexadecimal digits.
Blank lines are not permitted. The decode process must accept lines with between 2 and 1000 characters, inclusive. The original purpose was to select a channel on a paper tape loop controlling the printer. The first word after the EDI keyword indicates the particular interchange standard. The X.400 keyword specifies a section that is converted from an X.400 body part type not known to the gateway, or not corresponding to a useful internet encoding.