keyword

KEYWORD  -  assign a keyword to the outgoing message

Usage:  KEYWORD keyword-name

The KEYWORD command puts one or more keywords in the outgoing message.
  They will be placed in a header field called "keywords", and if your
  addressee uses MM or another mail system that uses keywords, he/she
  can use the keyword to locate your message later (for example, using
  the HEADERS command and the message-sequence "keyword").

To use CCMD completion with KEYWORD, see help for SET KEYWORD.

Examples:
    Send>keyword bird         #assigns the keyword "bird"

    MM>header keyword bird    #The person who -receives- your message could
			      #use this command to locate it later.

For more help type "help" and one of these topics:
  message-tagging   unkeyword   set keywords   message-sequence
  headers   ccmd