General Wierdness

This general wierdness takes place in our office and was
wondering if anyone else has experience the same problem
and better yet if anyone has a solution.

We have an Exchange server 2000 which all the computers
in are offics use for their e-mails this includes both
Mac and Windows. For the Windows users they're using
Office 2000 and Outlook. For the Mac users they're using
Entourage 2004.

The wierd thing is we've had several instances where a
Windows user will received 2 e-mails from a Mac user who
is just sending a single e-mail out to them.
Interestingly, what happens is that the original e-mail
will come in first and then a second will show up where
the sender is the recipant trying to forward it to
another address.

I was originally thinking that this might be a virus or a
rule but cannot find or rule out either.

Something tells me though that it might be a bug in
Entourage as well as this only happens when Entourage
users send mail out.

If anyone has any thoughts or know of anything I would be
interested.

Thanks