Spoofing an e-mail address is trivial and thus not an accurate way to check for or block spam e-mails. ex. I can send an e-mail using your e-mail address as the From: and make the To: your mom, and make it look like you sent the e-mail to her. The only way to know, and still somewhat easy to spoof, is to check the e-mail headers and find the originating IP address. You can take that IP address and go to one of the popular spam blacklists, such as Spamhaus or Spamcop and see if anyone else has reported that IP address as sending spam in the past.