New feature in GMail

They started the 'try to unsubscribe me' service about a week ago. Hopefully it'll both be handy for users, and though losing subscribers is bad, I'd think getting an unsubscribe is better for your list than having it marked as spam in googles database.

Halsey

Just double checked, based on the updated stamp, a bit more than a week ago, from google help

Auto-unsubscribe - Gmail Help

Auto-unsubscribe
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We don't think you should be burdened with managing messages you don't want to receive. We do our best to put messages in Spam when we're pretty sure you won't want or need them. But everyone has different preferences about the mail they want to see. You may not want to read any messages sent by a certain company or mailing list, while another Gmail user finds these same messages to be valuable.

To help solve this problem, 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!

Keep in mind that mailing lists may take up to three days to process your unsubscription request, so it may take a few days for you to stop receiving mail from the list. Also, please note that we are unable to provide the Unsubscribe option for all mailing lists. For your protection, Gmail won't display Unsubscribe for lists that are known to be owned by spammers. When you don't see the unsubscribe tool for a particular newsletter or mailing list that you trust, check the actual message for unsubscribe options, or try contacting the list owner about removal (you should only do this if the list owner is trustworthy and not a spammer).

updated 7/17/2009

I knew I loved Gmail for more than one reason. I will find this option very useful I'm sure. I don't mind ads, when I ask to be added to a list to receive them, but I can't stand spam, especially when it is something useless.

Thanks for pointing this out Bev!....

I continue to see advantages in Gmail over Yahoo and others. ...features like this are one reason. I'm also impressed with their spam filters. They seem to know exactly what is and isn't spam - much better than Yahoo.
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Bruce Ruby