We are organizing periodic surveys and we would like to make sure that we dont send invitations to people who dont like to recieve them (even if we go through double opt-in process some users after sometime get bored of surveys and instead of unsubscribing start marking emails as spam). So to indentify such users and drop them from the mailing list we would like to subscribe to \'feedback loop\' information from google.

Google provide a possibitlity to recieve such feedback but an additional hearder( List-Unsubscribe header) should be sent in a email.

An additional header information should be send with all email invitations/reminders.

The same feature can work with many mailing systems thus enabling to recieve feedback from many survey participants.

More information about the technical aspects:
www.returnpath.net/blog/intheknow/2009/0...-mailing-lists/#more

General feedback loops:
en.wikipedia.org/wiki/Feedbackloop%28email%29