Last month Gmail introduced a new "Unsubscribe" link at the top of emails in your inbox. The purpose of this is to make it easier for people to unsubscribe from mailing lists they're on, without searching in the email footer for the link. The more easily people can unsubscribe, the less likely they are to click the "Spam" button, which hurts your sender score.
Here's an example of what it looks like:
This link is generated from the "List-Unsubscribe" email header, assuming the sender has authenticated the email with a DKIM signature. If you don't know what DKIM, trust me that it's very crucial for email deliverability. You can read more about it from the horse's mouth.
Without any major announcement, Gmail rolled out a new feedback loop, that let's email service providers (ESPs) know if their recipients have been clicking the "Spam" report button in Gmail.
By using a special email header called "X-Feedback-ID", ESPs can tell Gmail which user and campaign sent each email, and on a daily basis, Gmail emails them a CSV file with the results of the worst-performing campaigns. Interesting system, it sounds like it's still too early to tell how effective it is. But it's something to be aware of, especially if you use any of the common ESPs.
Kane Miller from Winning.Email
Kane has a background in computer engineering, but now focuses on creating new and interesting web services. His passion for improving his own email deliverability rates was the driving force behind the creation of Winning.Email.