Important communications should go through multiple drafts. That includes important emails. Write it all out, then re-read it carefully, ideally after a bit of time has passed. Edit with an eye toward making it shorter. Rewrite it from scratch if you have to.
I once had the good fortune to take a writing class with Edward Hoagland. We spent most of the semester with each student working on a single essay--reviewing it, editing it, rewriting it, rewriting it.