When LISTSERV (1.5n) gets a file in its reader that it can't handle
(mail with bad header, list with bad password, etc), it transfers the
file (at our site) to MAINT.  Since VM/HPO 5.0, >>sometimes<< this
transfer fails and the file remains in LISTSERV's reader.  So it comes
up again, he transfers it again, it fails again, etc., etc., etc.
 
Each one of these cycles of failure includes warning mail messages to
MAINT, POSTMAST, etc., with the result that rather quickly the spool
area fills up with these warning messages.  Once the spool area over-
flows, MAILER dies.
 
As I said earlier, it doesn't always happen.  In fact I resubmitted a
"bad" file to LISTSERV while signed on as LISTSERV so that I could watch
what was going on.  It immediately transferred the file successfully to
MAINT.