They do in a way, the 'List-Unsubscribe' header: https://support.google.com/mail...

		jspaur on March 6, 2013 \| parent \| context \| favorite \| on: Preventing Unsubscribes in Forwarded Emails They do in a way, the 'List-Unsubscribe' header: https://support.google.com/mail/bin/answer.py?hl=en&answ... Appears to work with Outlook.com/Hotmail, and Gmail. Not sure about Yahoo, but those two alone cover a pretty big group.