Hi. The code you are looking for is in LSVXMAIL EXEC, and looks like:
 
 If Left(subj,9) == 'UNDELIVER' |,       /* Crosswell or FAL */
    Left(subj,22) = 'UNABLE TO DELIVER MAIL' |,   /* Mult*cs */
    subj = 'RETURNED NETWORK MAIL' |,   /* VAX-type  MAILER */
    pos('FAILED MAIL',subj)>0 Then      /* cern Mailer */
    Call RejMail 'mail subject indicates a delivery problem'
 
Note: I added that FAILED MAIL part - that line is not part of the original
code..  -turgut