I think it's sadly a bit of a chicken and egg problem, unless someone sets out to write support for servers (mostly dovecot I assume) and clients (web and deskt

I think it's sadly a bit of a chicken and egg problem, unless someone sets out to write support for servers (mostly dovecot I assume) and clients (web and desktop). It would be worthwhile for many reasons not just the immutable IDs. I'd certainly donate to someone showing initiative working on this.