This feature was introduced in 1.7f, not 1.8a. The change in behaviour is
due  to LMail  1.2a  which translates  FAL delivery  errors  to a  format
LISTSERV  can parse  and  allows  most delivery  errors  to be  processed
automatically. You can turn this feature off with "Auto-Delete= No". Note
that only  hard errors  cause deletion.  Some systems  incorrectly report
temporary errors as hard errors but there's nothing LISTSERV can do about
it.
 
  Eric