[wiktor-k]

> To be frank I quite like this idea. Can’t we standardize it somehow and add it to other email clients too?

Just copying what I said in the other thread: there actually is a standard for that already: https://datatracker.ietf.org/doc/html/rfc9078

Sadly, it seems it doesn't have broad adoption: https://bugzilla.mozilla.org/show_bug.cgi?id=1724363