I know there is block user option to limit spam or abuse. Since each post has unique message id, is it possible to flag or block that particular message thread using message id instead of blocking user. This option is for user side. This would be the solution to stop spam for a particular post replies without user id. One option I can think of would be to set the expiry date to the message id, so email piping or messaging no longer works on that thread once that message id is expired or user set the message id to expire.
Also how to hide message id from the subject line, but still use it for email piping? I assume if user change this message id in the subject the email to email reply wont work.