I need this feature in gmail that I saw discussed on Lifehacker.
You can also set up your inbox to only keep a certain number of new messages from one sender—or rather, automatically delete all newsletters except the newest one from a given sender. It's all really well thought out, and perfect for keeping up on those newsletters without creating extra inbox clutter.
I get a lot of ads from Amazon, Best Buy, Barnes and Noble, Audible.com, Micro-Center, and others that I do want to see. I do see things that I want to buy, so I do not want to unsubscribe or automatially delete them. After a week or two though I would like them to disappear.