Strange mail bouncing

[peterjoel]

A large number of people are finding that their mails to me bounce back. It's always the same people, but it's about half of the people who try to send me emails.

For example, if I send a mail to myself from work, I get bounces like this:
(I modified the email addresses)

The original message was received at Mon, 27 Feb 2006 11:11:21 -0500
from MSGMROSM02WIN.dmn1.fmr.com [172.26.31.170]

----- The following addresses had permanent fatal errors -----
<[myname](at)peterjoel.co.uk>
(reason: 553 sorry, that domain isn't in my list of allowed rcpthosts; no valid cert for gatewaying (#5.7.1))

----- Transcript of session follows -----
... while talking to www.peterjoel.com.:
>>> DATA
<<< 553 sorry, that domain isn't in my list of allowed rcpthosts; no valid cert for gatewaying (#5.7.1)
550 5.1.1 <[myname](at)peterjoel.co.uk>... User unknown
<<< 503 RCPT first (#5.5.1)

The error notification comes with my original email attached, but with the address changed to [myname](at) www.peterjoel.com


I have my Apache configured to forward http requests from my .co.uk domain to my .com domain. I also have mail forwarding set up in Plesk from peterjoel.com to peterjoel.co.uk, so that could be related. But I don't have any mail settings that mention a www domain.

Any ideas on what is happening?