I have noticed a header in use these days. It is "List-Unsubscribe". When this header is used in sending email then email client can use this to unsubscribe you from the mailing list.
I have another desktop email client called "Windows Live Mail", but it not using it. In online Gmail client, when you click on the link visible after clicking on "show details" link, you will get a message: We will attempt to unsubscribe you from this sender.
When you click on spam button for this kind of email then you will get a helpful message to unsubscribe with options: "Unsubscribe and report spam" and "report spam". It is very useful.
Header is added inside email in this format:
so, if you send email list then I hope you use this header to help other to unsubscribe from the mailing list. This is far better than free email service provider mark all your email to spam by default.