strange bounces

[James E Wilson <wilson@specifix.com>]

Since no one seems to know what the problem is, I tried looking for
info, and found an interesting thread on the nntp.perl.org server in the
perl.qsmtpd mailing list, with the subject line "Strange bounce problem"
sent on Nov 4, 2004.  Since there is no convenient URL, I've quoted the
interesting parts of the most interesting message:

I don't know if this might help, but I just spent hours with ethereal
and
full debugging on all the servers and here is what is happening:

telnet server 25
220 server ESMTP qpsmtpd 0.28 ready; send us your mail, but not your spam.
503 MAIL before RCPT
503 MAIL FIRST

Now, looking at the tcpdumps reveals that you in fact never sent anything,
however, if you look at the logs you see that the server was dispatching
something like : RCTP TO: <thisuser@thisdomain.com>, back to ethereal and
you can see that sure enough a server sent that packet a good 10-15
seconds ago but was denied with the require_resolvable_fromhost.  What
seems like is happening is that Qpsmtpd is dropping the connection but the
buffers aren't being flushed so that when the next Qpsmtpd picks up the
file handle the old one had it's getting the data that was left over. 
I am running Pperl with --no-cleanup but enabling cleanup did nothing to
solve the problem as did just calling qpsmtpd directly from tcpserver
without pperl.  The only thing I have found that got rid of the problem
was to edit the require_resolvable_fromhost plugin and change it from
DENYHARD to DENYSOFT.  Hope this helps somebody out there.

Ed McLain

End quote.

There are also some other related suggestions in other messages in the
thread, but this one seemed like the most useful.  You might want to look at
the entire thread.
-- 
Jim Wilson, GNU Tools Support, http://www.specifix.com