[exim] Outlook / client problem or misconfiguration? - from …

Hi,

A few days ago, one client migrated to our mail services, everything ok,
however, after the move was completed hell came down upon us.
It seems mail delivery has been broken ever since.

What happens is that Exim works fine, at least, I think it does, but
after they fetch the mail (Outlook) by using POP3 (vm-pop3d), some
process just seems to add something to the original header. Outlook
doesn't understand it, but hey, it's a message, so it display's the
message source.

What I mean is this;

If I would mail someone at the domain, mail gets delivered, they fetch
it by POP3, and between the fetch and the delivery in their mail client
this happens:

*>*From xxxx@??? Mon Dec 18 13:50:03 2006
Return-path: <xxxx@???>

It adds an > to the From header, so it's no longer recognised by Outlook
as valid.
This happens every time a mail get through.

Personally I think the problem is caused by the virusscanner they use,
however I don't have any data on it. Today I'm going to ask them if they
can shut down their virus scanner for some time, so we can see if the
problem goes away...

Has anyone had this problem before, or does anyone know a solution to this?
I understand it most likely isn't caused by Exim (as Exim works great on
all other domains), but if anyone of you have an idea, I'm really open
to it, right about now ;).


Thank you,