Find The Originating ISP Of An Email

A tip from Windows Secrets:

Here's how to find the originating ISP of an e-mail:

• In Gmail, click the down arrow next to the right of the message header (next to the Reply button) and choose Show original. That shows you the entire message, including the full header information (the message routing information at the beginning of the message, which is normally hidden).
  
• Copy the entire header and go to the ipTRACKERonline header-analysis page.
  
• Paste the header info into the Email header analysis input box and press the Submit button.
  
• After ipTRACKERonline reloads the page, scroll down to the Email header analysis report box. There you'll see where the message has been and — most of the time — where it originated.