The email reply trimmer trimmer is doing a good job and is being improved where possible but given the real world of email signatures, it’s never going to catch every signature. So how about making it so that if someone edits the post to add some code (perhaps simply --), this will be recognized as the correct cut-off point and the post will be rendered accordingly?
Intended usage is simply to make it easy for staff to hide a signature when they come across one (without deleting it).
Edit: I just tried whether this perhaps already works: I inserted -- at the beginning of a line in a reply-by-email post and triggered a “generate HTML” but nothing happened. So I guess to make this work, the “generate html” routine would need to see that this post is a reply by email and understand what to do with a -- in this context (not in ordinary replies).