I found out from returned "undelivered" email that those address does not exist in my lists--in the first place, I have never sent them

Unfortunately there is not much we can do about e-mail spoofing as it’s achieved by changing the reply to e-mail address in a mail client. This makes it seem like the e-mail is coming from an address that it’s really now.

Many affected owners of email domain being spoofed are complaining of having their account being suspended for spamming and receiving "tons" of harassing hate mails marked as coming from them--which they have never sent and only found-out when they start receiving angry replies or returned undelivered bounce email.

The victims of these new from of harassment in which fake or boogie messages was sent-out posing as the original owner of the email address by spoofing, are usually done by dissatisfied or fired employees, competitors, pranksters, junk mailers, provocateurs or spammers trying to sell something--not that they want you to respond to the email but to click on a link in the message.

According to the FBI, spoofing is generally not illegal because no hacking is required, unless it involves a direct threat of violence or death and by using such tactic, know as email spoofing--they exploit the simplicity of Internet SMTP (simple mail transport protocol RFC 821). Email can be spoofed by tweaking the settings on standard email client like; Eudora, Outlook Express, etc.

There are also many website that offers an automated process for creating and sending spoofed email by inserting someone else email address into the Mail FROM: or REPLY TO: fields--which also contains information about the "origin" of the message--but most people don't know how to decipher it or simply assume that the spoofed message is genuine.