Great tip from Alex at DiscoTank: Use "Bounce" in Mail.App to reduce or eliminate spam.
Basically, Alex suggested taking all of your Junk mail, and sending "bounce" messages to the servers. Many spammers use auto-generating server tools which remove addresses that return a bounced email address (not that the spammers actually care, per se, but they are set up that way to lower the overhead on the servers). So, by sending the bounce message, the spammers server may/should remove your email from their list. AWESOME!
- Right click in the toolbar, click customize toolbar. Drag and drop the “Bounce” button into your toolbar. Close customize toolbar.
- Make sure you have enabled the “Junk” folder. You can do this by clicking Mail>>Prefs>>Junk Mail>>”Move it to the Junk Mailbox (Automatic)” and Save.
- Go to your Junk mailbox, and highlight every message (CMD-A).
- Hit “Bounce”, an alert will come up, click okay. The messages are deleted once they are bounced.
That's it. With any luck, you'll get a few less junk messages a day.