The 'mesg' command

Usage: mesg <command> [mesg. no.]

where command is one of :

EDIT    - edit the main text of the message 
TO      - change the To: field of the message
SUBject - change the subject field of the message
DELete  - mark the message for deletion 
          (will no longer be shown to normal users)
UNDELete - remove deletion mark
STatus  - adjust message status [Deleted,hasReply,eXternal,Moderated]
