It's looking like we could be able to hyperlink to emails soon! No more of this "oh uh check your email for the one I sent at 11:27...". You'll be able to add a link that works just like linking the web!
The IETF is working on their "Parsable Mail Pointer Email Protocol" (PMPEP), and I was able to get an advance copy! Check it out below:
RFC 9869: Parsable Mail Pointer Email Protocol (PMPEP)
Personally, I think they backronymed it from "Per My Previous Email Protocol"...
Edit 4/11: Yes, this was a joke. And apparently it would indeed be enough just to use the messageID. So why hasn't anyone implemented this???