Ken Manheimer <klm@cnri.reston.va.us> writes:

There is a known bug in some recent versions of sendmail (8.8.x for some x, and 8.9.0) such that the sendmail will core dump when attempting to deliver mailman's (or any 8-bit encoded) Mime-format digests in certain (somewhat uncommon) circumstances. The question then is, were the messages that never appeared in the users mailbox Mime digests? And if not, could you construct a repeatable test that at least reduces the likelihood that the problem is on the receiving ends? For that matter, might you happen to be running sendmail 8.8.x or 8.9.0? Your sendmail may be getting so far as negotiating the delivery and then failing partway through...

He should check his mail spool. If sendmail dies, it leaves the undelivered message to the spool, which then starts to gradually grow.

When I had a broken sendmail, most of the messages still went through.

-- Janne