Buttondown Documentation
We sure do!
We use one-click unsubscribe headers (also known as List-Unsubscribe headers) in every email we send to make it easy for clients like Gmail to automatically detect and display an unsubscribe link in the email header.
If you're analyzing the headers of a preview or draft email, you won't see the List-Unsubscribe header. This is because the header is only added when the email is sent out to your subscribers. Previews are technically transactional and don't get all the same headers appended to them as a regular newsletter email