> 2. It states that subject prefixes like “Re:” have no technical relevance. That’s not entirely true, because email clients recognize existing prefixes when re

> 2. It states that subject prefixes like “Re:” have no technical relevance. That’s not entirely true, because email clients recognize existing prefixes when replying/forwarding, in order to not add a redundant one. Sort of. That can just be a clever regex. There is a In-Reply-To header that may actually give some suggestion on if this is a reply to something by telling you what it's a reply of.