Forum OpenACS Q&A: Re: New message header format causing spam
Are there any plans to implement the In-Reply-To header?
In-Reply-To headers require a redesign of the notifications package. Our recent changes improve upon the headers but can't achieve everything without an overhaul of the notifications package.
Such an overhaul would require all packages that depend on notifications to change too. Matt mentioned that he would like to further improve notifications but I don't know what his time table is.