A fine way to do it as lightly as necessary. A few things I’d consider to use it myself:<p>- mailbox-side filters to shove unsub and sub requests into folders. Then, the state discovery would read from those folders. This moves a little configuration into the server-side filtering (“Settings” in most webmails) so that I can pick up, for example, requests in non-English.<p>- Automatic subscribe requests would end up in their own folder, where To: addresses are the receiver. For a message to hit this folder, its filter needs to match an admin email.<p>- Non-requests from people would not end up in those folders, and I would accumulate those as reactions or comments —- collected as a comment-section for the next newsletter.<p>- Templating is helpful because there are laws around mailing list content. Perhaps more importantly, a mailto: link in the list-unsubscribe header.