I've always assumed when I hear people talking about AI emails, they're talking about longer formal writing to groups, such as a proposal not personal 1:1 messages. Hearing this kind of surprises me but I don't know first-hand since I was able to retire just before LLMs became ubiquitous.

In my experience, 1:1 or 1:2 emails among coworkers, peers or friends tended to be as short and direct as possible anyway. Even pre-LLM, an email as long or structured as an LLM would create today would have been notably weird.