Here is an incredible Gmail tip to quickly unsubscribe from all the companies you may have unknowingly subscribed to.
Open Gmail in a web browser.
Delete everything in the URL after /mail/ and replace it with /mail/#sub
This will open a list of all the companies you are subscribed to for emails, together with an unsubscribe button for each one.
The URL was accessable, The list was legitimate and I was able to unsubscribe to roughly 50 companies/lists on a fairly old email address. I don't know results, such as if unsubscribing works, but it looks to be a useful tool. Props.