Ratilal, the reason LISTSERV looks in the body of messages is that
there are mailing systems whose error messages can only be detected that
way.  Typically, they use unpredictable subject lines and don't bear
return addresses which are detectable as mailers.  In fact, sometimes
they just spit the message back with no indication that it is an error.
LISTSERV is just being cautious.
 
--Mark