http://www.sitepoint.com/article/sabotage-coping-joe-job
If you’ve ever had anyone spoof your website email and spam people in your name, you need to check this out:
Essentially, a Joe Job is a very crude form of identity theft. Your email address is used as the “sender’s address” in most cases, and your Website URL is advertised, but an especially diligent and vicious attacker may even use your name in the signature of the message. The email will not only be sent to thousands, hundreds of thousands, or millions of addresses, but it will be sent multiple times — possibly dozens or hundreds — to each recipient before the attack ends.
Dillian Thomas from BoxedArt.Com writes a great article with what you and your clients need to do to protect yourselves.
(Btw… that’s JOE job, with a “J“… you don’t want one of these. trust me.)