When you receive a bounced email, it's simply the destination server letting you know that the account you're trying to reach doesn't work. It's the email equivilent of the message you get when dialing a number that's no longer in service.
When you bounce an email, Mail does its best to duplicate that type of message and send it back to the original sender. For the casual email it will probably fool them into thinking that your email is no longer valid. If you try using it on spammers, they may not be so easily fooled... so take your chances with them.