[jasonjayr]

I understand that the request happens in the background by the MUA at the user's express consent, and the unsubscribe is not allowed to send back any ui/html/whatever to present to the user, but the RFC is missing any information about how a response ought to be handled, HTTP Status code wise? Retry if 400/500? Give user any affirmative or negative response that it succeeded or failed?

[chuckadams]

That's up to the MUA, but I imagine that they would at least show an error dialog. If the backend of that POST is broken, then the spam complaints are going to rack up, which will get the list blocked, List-Unsubscribe header or no (some of the most notorious spammers around were actually quite scrupulous about having said header, which they would actually obey ... temporarily)

[zie]

You can't send back anything? oops. I better re-read the RFC's, that's not how I implemented it...