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Build a "writes in my voice" content coach from your sent mail

Generic AI writing sounds like generic AI. Build a no-code agent grounded on your own sent mail so it learns how you actually write — then have it draft and coach in your voice, not a robot's.

Stage: Agent Builder · For: Maker, End user · Level: Intermediate · Time: 20 min

When to use this

The fastest complaint about AI-written text is that it doesn't sound like you. But you have a huge corpus of your real voice sitting in Sent Items — every email you've ever written, in your phrasing, your rhythm, your level of formality. A personal-scope declarative agent can ground on that and become a content coach that drafts and edits in your voice instead of flattening it.

Use this when you want AI help with writing but keep rewriting its output to sound like a human — you.

What you'll need

  • M365 Copilot license with Agent Builder (Copilot → Create an agent)
  • Your Sent Items (or a representative folder of your writing) for the agent to ground on
  • 20 minutes and the four ingredients: name, instructions, knowledge source, starter prompts

Try it now — the build

In the Agent Builder conversation, describe a coach that studies your style:

Create an agent called "My Voice" grounded on my Sent Items. First, learn my writing
style from how I actually write — my tone, sentence length, how formal or casual I am,
phrases I use, how I open and close. Then help me two ways: draft new messages in that
voice, and rewrite drafts I give you so they sound like me, not like generic AI. When
you rewrite, briefly note what you changed and why. Never invent facts — if you need
information I haven't given you, ask.

Why this works: it grounds on the best possible source of your voice (your real sent mail), tells the agent to learn the style first (tone, length, formality, signature phrases), defines two clear jobs (draft + rewrite), asks for a short rationale so it's a coach not a black box, and sets the no-fabrication rule. Voice comes from real examples — that's why grounding on your own writing beats any "be friendly" instruction.

Step by step

  1. Open Agent Builder. In M365 Copilot, choose Create an agent. Build by chatting or use the Configure fields.
  2. Add the knowledge source. Point it at your Sent Items (or a folder of your strongest writing). This is what it learns your voice from.
  3. Write the instructions (the prompt above, adapted). The "learn the style first, then draft and rewrite, explain your edits, never invent facts" sequence is the whole trick.
  4. Add starter prompts for the two jobs: "Draft a reply to this in my voice: …", "Rewrite this so it sounds like me: …", "Is this on-brand for how I write?"
  5. Test in the preview pane. Paste a stiff draft and ask it to rewrite in your voice. Read it aloud — does it sound like you? Tune the instructions until it does.

Screenshots

We deliberately don't ship screenshots that go stale — the Microsoft Copilot UI changes often. Follow the numbered steps above, which we keep current. Maintainers can regenerate fresh captures with the Playwright tool in tooling/screenshots/.

Make it better

Sharpen the coach over time: - Name your own rules. "Here are three things I always do and two I never do — bake them in." - Flex the register. "Give me a more formal version for an exec and a casual one for my team." - Make it teach you. "When you rewrite, point out one habit of mine that weakens the message so I can improve it."

📚 Learn more. Browse Microsoft's Agent Library for templates, and watch April's AI Agents Academy (April Dunnam, Microsoft) for step-by-step building.

Watch out for

  • Voice, not facts. Ground it on your sent mail for style — but never let it carry over real names, numbers, or commitments from old emails into a new draft. Tell it explicitly: imitate the voice, not the content.
  • Keep it strictly personal. This agent is trained on your private correspondence. Do not share it — another person's drafts shouldn't be filtered through your inbox, and yours shouldn't leak.
  • You're still the author. A voice match makes bad advice sound like you. Read every draft as the person whose name is on it.

Where this leads (the ramp)

You built a personal agent that generates in your style. Its ceiling is that it only writes — it can't pull a live figure, post to a system, or run a designed workflow. When you need an agent that does things, not just drafts them, you move to Stage 6 · Copilot Studio.

Next: Copilot Studio → Build your first Studio agent with a knowledge source + topic

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