Exchange 2003

Ok, my turn. I have an Exchange 2003 server and I have a couple of instances where a PDF attachment is getting stripped. This is when one of my internal users sends out. But when the user sends to my external email, I get attachment just fine.

I am also running GFI Mail Essentials, but as far as I know, thats only monitoring inbound.

Is there way that I can prove that my server is seeing the attachment and sending it one? i am 99.999% positive its on the destination end.

Thanks!