To product designers: In practice, you should really avoid using the "sending a reply email message" part. Especially these days when people have multiple email addresses, it can very quickly break down.

This happens often to me:

* Get email that I'd like to unsubscribe to

* Look for unsub info -- directed to "reply to this email" or, almost as bad, "enter your email address"

* Follow instructions

* Receive notice saying "Sorry, the email you entered [sent from] is not in our database"

Well thanks. We've gotten nowhere.

So the right way to design this should be a simple unsubscribe link w/ a unique token that executes the request upon clicking.

At worst, you can do what Constant Contact does and require the email address to be entered, but still provide a hint (i.e. "a....c@gmail.com"). This is still somewhat annoying, but I understand why they do it -- it likely reduces net unsubs since there's a second step involved. Pushing it, but thinking as a business owner as well, I get it.