Weird problem with exim4 and Sympatico

Hi.

I posted on comp.os.linux.misc about this, but didn't get much
help.

I run a Debian Sarge box with exim4 as my MTA. The box is connected
to the Internet via a DSL account from execulink. I have a domain
name (faustus) provided by a dynamic IP name hosting company called
dyn.ca.

I prefer that mail be sent directly to my box, hence my email
address is USERNAME@faustus.dyn.ca. I have been using this setup
for months, with no problem. All email sent to that address goes
through--except, very specifically, HTML formatted email that is
sent to it from someone else's Sympatico account. Plain text email
from Sympatico accounts reaches me just fine.

(Please--no rants about html email. I'm against it, too.)

I realize that exim doesn't filter content, so it one would think
exim couldn't be causing the problem. Yet the only indication I
can find in my logs of html email not getting through is in lines
of the form

2005-09-12 08:50:23 SMTP data timeout (message abandoned) on connection \
from bayc1-pasmtp02.bayc1.hotmail.com [65.54.191.162]

(The above definitely comes from the Sympatico account of someone I
know, regardless of the "hotmail" bit.)

I have set up the exim router/transport to use the procmail_pipe,
but procmail doesn't seem to be the problem either. My .procmailrc
is vanilla, and set up to bounce nothing. Besides, my procmail.log
isn't showing any bounced messages.

Does anyone have any idea why, specifically, Sympatico-sent html
email isn't reaching my machine? I can't provide email headers for
forensics on this, since--obviously--the bounced emails go back to
the Sympatico users who sent them.

The only other bit of information I think needs to be stated is
that I, myself, am NOT a Sympatico subscriber. Not at all; never
have been, never will be. The issue is not email that I send being
returned to *me*, but email (html email, that is) Sympatico
subscribers send to me being returned to them.

Any and all help appreciated, even if it's just to point me to a
better newsgroup for posting this kind of problem.

--
Peter Schaffter
Author of _The Schumann Proof_ (RendezVous Press, Canada)
http://faustus.dyn.ca