This was such an improvement to mine as well. Lots of strange advice in this thread about "one sentence/question per email" and other arbitrary terseness. Just use a messaging system for single-thread async communication.

Writing the email is part of the thinking process for me so by the time I finish there is a single coherent sentence that I can cut-paste to the top with the rationale/evidence/etc organized below it. If the one-liner is enough they can skip the rest (which I needed to write anyway regardless) and if they need more detail they don't have to ask.

Some other practices I've picked up over the years:

Responses should always be inline between relevant quotes rather than the default of hiding the original at the bottom. Remove quotes that don't matter. My favourite responses are a simple "Agreed." after a long quoted paragraph of justification.

In general the email chain should get shorter with each reply otherwise it suggests that the topic is either too complex or insufficiently defined. It also gives some sense that it will eventually end!

Write subject lines that make searching/filtering easy to do later rather than something to catch the recipient's attention.