[cowlby]

This x100. I move it all to a folder called “Unsubscribe” and go through and unsubscribe from everything once in a while.

You can also make it a bit smarter by searching for the header “List-unsubscribe” instead. Less false-positives when someone forwards you an email that contains the word unsubscribe.

[bityard]

You have to be a little careful about this. That works for semi-ethical marketing departments, but for actual spammers it can send a signal that there's a warm body behind the email address, making it far more valuable and more likely to receive even more spam in the future.