The following is for Gmail users only. Do you receive email messages from spammers or even from legitimate companies that apparently are using mailing lists? You know the type: you get a message or two most every day. It is full of advertising, probably ads you could not care less about. At the bottom of the list, there is a statement of "click here to unsubscribe" or something similar.
Personally, I’m always leery of clicking “unsubscribe” from spam emails I receive, because I’ve found they typically end up creating even more spam. It also irritates me to think that these folks expect me to take action to unsubscribe from their junk when, in fact, I never asked for it in the first place.
Now Google has invented an "automatic unsubscribe" feature for Gmail users. It requires very little work to unsubscribe: one mouseclick when reading the unwanted message.
According to the Gmail Auto-Unsubscribe instructions at http://mail.google.com/support/bin/answer.py?hl=en&ctx=mail&answer=80405:
…we’re providing you with an unsubscribe tool for some messages. You’ll see the unsubscribe tool when you mark a message from particular types of mailing lists as spam. If the particular message is a misuse of a mailing list you like to receive, you can Report spam as usual. But if you never want to receive another message or newsletter from that list again, click Unsubscribe instead. We’ll send a request to the sender that your email address be removed from the list. It’s that simple!
I am not sure this works on 100% of the unwanted messages. In fact, I don't know how it works at all and Google apparently is keeping the inner workings a secret in order to keep the information away from spammers. However, I'll settle for even a percentage reduction in unwanted email.
You can learn more at http://goo.gl/Rn0Q1