Sure, keep it short. Yes, yes, yes: we know that.
But why?
- It makes it easier for the reader to understand and absorb and thus you are more likely to get the response you require quickly.
- But more importantly short means we the writer need to get our thoughts organised: what do we really want, why are we really writing? Shorter we means we have gained clarity about the situation. And thus again we are more likely to get what we want and quickly
TBC
In the meantime: How To Lessen E-mail Pain