There are two problems. The first one is that these mail messages usually
do NOT have an empty body - they  have a body with just the .sig file. If
you require an empty body (only blank  lines), you will still leave a lot
of users disappointed (many don't know  how to turn off the signature, or
forget). The second problem is that if the 'Subject:' line is present but
contains an invalid command (with the actual commands correctly placed in
the mail  body), the  job will be  flushed with an  error message.  It is
quite difficult to prevent this from happening if the invalid command was
the one  in the 'Subject:' field,  and even more difficult  to remove the
error message resulting from finding out that it is invalid.
 
  Eric