send non-delivery notification
I am fairly sure MobileMe (and possibly Mail.App) had a feature which allowed you to send a non-delivery notification for an email. This is possibly the best way to battle spam, however I can not find this feature anywhere now. Has it been removed or is it hidden somewhere else?
Solution 1:
This page suggests that the feature exists in Mail under Lion. The feature, however, does not appear to exist, either as a toolbar option, nor as a Message menu command, nor as a context menu command, nor as an item in the Help file for Mail. The aforelinked document says "Lion" in its title, but refers to Mail 4.0; the Mail program under Lion is Mail 5.1.
This may or may not have anything to do with Apple's acknowledgement that bounce does not always dissuade spammers.