Exchange displaying header info in body of message

Hi All,
I posted on this recently, but didn't get a response.

This is how the situation is set up.

There is a parent company estatemanagers.com who hosts all of the email for
all of the branch franchises.
Estatemanagers.com holds the email for pop access only.

Our company looks after one of the franchises, who has an SBS 2000.
This server uses the pop connector to download emails from the head office.

As of about a month or so ago, something changed and emails became garbled
displaying header information in the body of the message.
The weird part is that, not all emails come in garbled, only email that
comes in from other franchises via the main office.
We are the only franchise that uses a mail server.
Everyone who isn't part of the franchise that we look after is sending via a
pop account set up on their laptops/desktop Outlook 2003 clients.

So far, I have tested using a different 3rd party pop connector (popcon) for
the incoming emails, this made no difference.
I have tested having the emails come in while the antivirus email scanning
services were stopped (Trend Micro CSM 2.0). That made no difference in the
outcome of the emails.
I temporarily stopped the pop connector service on the SBS 2000, and set up
outlook 2003 client with an account to pop the emails from the head office
directly, this displayed the email messages without the headers overflowing
into the body of the message.

So from that I am assuming that the problem happens when the email messages
touch the information store.

I have looked at the header information on the emails when they come in
corrupted, the part that it still uses as the header anyway. After the
'Date: ' header is two CRLF's, two returns.
And after that, all the rest of the header is displayed as body text.

I need to get this problem fixed, i have alot of angry email users that feel
they can't communicate within the company using email any more.

What can i do to further diagnose this issue?


Things that have happened recently:
- Exchange hotfixes have been reapplied to fix an SSL issue causing errors
in TREND antivirus web console.