[Exim] Mailing list rejection problem

Hi Folks.

I'm using Exim to run a little personal mailing list, configured as
explained in the documentation "Using Exim to handle mailing lists".
It's working fine in most cases, but I do have an intermittent problem
with one of the users on the list. I'm getting the following entries in
the Exim maillog file :

1999-10-26 12:38:34 11g9Nw-0003pN-00 ** ian.hannaford@???
<lee-list@lists
.shakey.org> R=lookuphost T=remote_smtp: SMTP error from remote mailer
after MAI
L FROM: <lee-list-request@???> SIZE=2633: host
butler-se.pnu.com [1
93.235.229.100]: 500 Command unrecognized: "\001\001\b"


Unfortunately, it doesn't happen all the time. In fact about 70% of the
messages get though without any problem. :

1999-10-26 12:45:11 11g9ha-0003rl-00 => ian.hannaford@???
<lee-list@lists
.shakey.org> R=lookuphost T=remote_smtp H=butler-se.pnu.com
[193.235.229.100]


Both the above examples were sent from the same person, using the same
MUA via the same relay (Netscape for WinNT via Sendmail). One gets
through the other doesn't. The butler-se.pnu.com machine appears to be
a Sun box running sendmail 8.8 so I don't think that the problem lies
there and its not multihomed either so I think that I'm talking to the
same machine each time :

220 butler-se.pnu.com ESMTP Sendmail 8.8.8+Sun/8.8.8; Thu, 28 Oct 1999
15:23:45 +0200 (MET DST)


It looks like Exim is putting something nasty in the SMTP conversation
and sendmail is rejecting it, but I haven't seen anything like this
before and don't exactly know how to proceed. Is there some way I can
make Exim log SMTP conversations just with this host?

Regards,
Lee.

--
Lee Shakespeare : lee@???