Reduce spam or get rid of unwanted mail!
A pretty cool function hidden in Mac OS Mail application is "Bounce". Basically, what it does is it resends the email to the sender and it looks like the message bounced back and the address doesn't exist. This can be useful to get off a mailling list that you're stuck in or simply for pretending you didn't receive a message you don't want. It can be added to the Mail toolbar by right-clicking on the toolbar and adding the "Bounce" icon to the toolbar. I tried it with both .Mac and GMail and it worked. Example: