The inimitable White Glenn received one of those obnoxious confirmation-bounces anti-spam software occassionally does these days. As a man of good taste and high ideals, he didn’t like it. How to avoid this problem with our hypothetical $MTP protocol? The only possibility I can see is over analysing all our email — if you get a reply with an In-Response-To: header matching an email you sent, or one whose From: and Subject: match a To:/Subject: you’ve sent.
Some more on why email challenges suck. A promising comment from that:
Any effective spam remedy must attack one or the other side (or both) of this equation: raise the costs or reduce the technological effectiveness, on the one side, or reduce revenues on the other.