As far as I can tell, there's no way to determine in a send-hook if the message is a reply. Is that right? This is the most obvious thing to try, but it doesn't work because ~h is invalid in the context of a send-hook: send-hook '=h In-Reply-To:' ... Here's what I'm using presently, but I'd prefer something more definitive: send-hook '~s "^Re:"' ... Thanks, Aron