This likely caused by the "passive" probe which is sent to a
fraction of the subscribership with each posting. If you don't want
the passive probe, you can add ",Probe(0)" at the end of your
Auto-delete line. If you don't want a particular user probed, you can
SET them NORENEW.

The passive probes are used for cleaning out users with mail servers
that use non-standard bounces (that go to the right address, of
course -- there's nothing that LISTSERV can do about servers that
send bounces to the wrong address). You will probably have noticed
that you are no longer getting the non-standard bounces.

Note that passive probes are only available in 1.8d.

If you are worried that one of the people who failed a probe
shouldn't get deleted, send them some e-mail and see if your mail to
them bounces, and if so for what reason.

Francoise