Facts, reader, voice
Brief it like a colleague
"Write a reply" gets a generic reply. Give the facts it can't know: what you have agreed, what you won't do, the deadline, and the outcome you want. Then say who the reader is and how well you know them. Three or four lines of brief beat any amount of rewording afterwards.
Show it your voice
Paste two or three emails you wrote yourself and ask it to match the length, tone and sign-off. Or write a short style note once ("short sentences, no exclamation marks, first names, get to the point in line one") and keep it in a Project or custom instructions so you don't retype it. Our prompt library has a Clone My Writing Voice prompt for building that note.
Tidying, not just drafting
Often the better use is the other way round: you write the rough version, AI tightens it. Ask for a shorter version, a softer or firmer tone, or a check for anything that could be misread. Keep your own words where they matter. A reader who knows you will notice phrases you would never use.
Before you hit send
Read every AI-drafted email in full. Check names, dates, figures and promises; AI happily invents a meeting on Thursday. Remove anything you wouldn't say out loud. And never paste a whole confidential thread into a tool your policy doesn't allow. Summarise the situation instead.
Open your sent folder and pick one email you were pleased with. What makes it sound like you: length, greeting, directness, humour?