If I have one I can't help but write, I'll add in a 1 line "TLDR" or "Executive Summary" at the top, then have details below. I do spend some effort to be funny or at least amusing in the long writing. Not sure how successful that effort is.

Even better is when someone writes a "help please" email that is long and has the answer to their problem in the original email (in a log message or something) and then it gets escalated and ends up with 50 emails "adding thus and so department/person" and then I get it, and read the first message, and can answer the problem.