Tracking mail passing through using non-adjacent domains

I would like to be able to easily report on the number if mail messages that pass through my mail.boxes from one domain heading to another. For example, mail from DomainA going to DomainC using me(DomainB).

Is there a database that I am missing? Activity.nsf does not give me the numbers I am looking for. It shows activity for the domain, but not what is passed from DomainA specifically for DomainC.

Thanks