"I'm not trying to find out how, but just whether or not there is a way to trace an email or a post to a forum back to the originating computer?"
It can be done. For instance, an email arrives at your machine. At the email server that you picked it up from, you would open its LOG FILE and see where that email can from. Next you for to that originating computer and look in LOG FILES there. Eventually you may find the source IP address of the machine that sent it and then you check who owns that address. If its some ISP like AOL, then they have LOG FILES that note what date/time and to who that IP address belonged to.
This forensic trail is possible to be done, but usually requires court orders and more.
Bob
I'm not trying to find out how, but just whether or not there is a way to trace an email or a post to a forum back to the originating computer? Thanks, Jerry

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic