Short emails are better
If you are dealing with a busy executive, a short to the point email is more likely to result in a response versus sending an essay.
Why is that?
Well - people are busy and it’s much easier to respond to a short well worded question than to parse through a long document. The longer a document is with the more information, the more ambiguous it is, the more time it takes to process and read the document.
Longer to read → Longer to process → Less likely to even bother replying
In fact long emails are just annoying to someone who is short on time.
Short and sweet is better - less time to write, less chance of saying something offensive, less chance of making a grammatical error. Better all around.