I've tested this before using several different email acounts and an open SMTP server I, uh...'found' , and I was always able to find my originating IP address. Since I knew what IP to look for it was pretty easy, so I guess it would be more difficult if you didn't know where this person was sending from...but it is possible to find the originating IP address, even from an internet mail account. But as s0nIc stated, if it's not a static IP, it really won't help you.