Sorry Instar, I couldn't locate anywhere on that site, how to trace the orginal source.
For those people reading this that have Outlook or Outlook Express and are interested, you can quickly look at the history of any email by :-
Outlook - 'Right click, Options, Internet Headers'
Express - 'Right click, Properties, Details'
Reading it can be a little bit more tricky, but reading the Received: lines, will give you an indication of where the email came from, and you should be able to find the IP address.
If you have an email from PBW, you should be able to use this method to determine that the email came from PBW and not the hosts email account.