Custom Instructions in Outlook: Copilot Writes Like You

Get the AI-speak out of your emails: teach Copilot your style

“Ever since I added your custom instructions, I actually enjoy writing emails with Copilot in Outlook!” That’s what a workshop participant told me. Their words, not mine. And that’s exactly the point: Copilot should sound like you, not like a machine.

The problem with AI-generated emails

Sound familiar? You have Copilot draft an email, and it reads like AI from the first line: “I hope this email finds you well.” “Please do not hesitate to reach out.” Stock phrases nobody would ever write on their own.

That’s not because Copilot is bad. It’s because it doesn’t know your style. The fix is custom instructions: you give Copilot a clear description of how you communicate, once, and it sticks to it. Microsoft lists the feature as “Custom Instructions for draft with Copilot” in its June 2025 release notes: you give Copilot guidance on tone, length, and greeting so drafts sound more like you.

Why custom instructions make such a difference

I use them myself. No more “I hope this email finds you well.” My emails sound like me again: direct, clear, in German, and free of filler.

You don’t have to write the instructions yourself. An analysis prompt does that for you: it reads your recently sent emails in Outlook and builds a profile of your writing style. What you get back is a ready-to-use set of custom instructions you can paste straight into Copilot.

And it’s structured so you can tweak and refine it yourself whenever you want.

The analysis prompt

Copy the prompt below into Copilot. Use the latest reasoning model (GPT-5.5 Deep Reasoning, or whatever is newest at the time), which you can pick in the model switcher in Microsoft 365 Copilot. That extra “thinking” gets you noticeably better results than the default model.

Important: This only works with a Microsoft 365 Copilot Premium license, and only in the Work tab. It won’t work with a Basic license or in the Web tab, because neither has access to your mailbox.

We're working together to improve emails generated by Copilot.

Step 1: Analyze my emails sent in Outlook over the last three months and use them to create a personal profile of my writing style, so an AI can adopt my style precisely and make email drafting easier for me.

Take into account:
- General tone (friendly, direct, formal, collegial)
- Typical length and content structure
- Frequently used words, phrases, and expressions
- Technical depth
- Concrete examples of greetings, introductions, main sections, and closings

Step 2: Also research typical elements that make emails sound artificial
or AI-like.

Result: Then create a set of Custom Instructions for Microsoft Copilot in Outlook in English, formatted as a Markdown code block. Include the following:
- General instructions so emails sound as human and natural as possible
- My personal tone, sentence structure, and typical phrasing from Step 1
- Explicit rules that prevent the AI-typical clichés from Step 2

Tip: If you write emails in more than one language, keep your instructions in English, as this prompt does. At the very bottom you’ll find my original prompt, word for word. It’s the one that’s gotten me the best results.

Putting the custom instructions to work

1. Open Copilot in the Work tab of Microsoft 365

2. Switch to the latest reasoning model in the model switcher (e.g., GPT-5.5)

3. Paste the prompt and run the analysis

4. Copy the custom instructions it generates

5. In Outlook, go to Settings > Copilot > Custom Instructions and paste them in

From here on, Copilot writes your emails in your style. Whether that works in your tenant is up to IT: if the “Enhanced personalization” control is turned off, Copilot doesn’t apply custom instructions, as Microsoft Learn explains.

Bonus: my original prompt

We're working together to improve emails generated by Copilot. Step 1: Analyze my emails sent in Outlook over the last three months and use them to create a personal profile of my writing style so that an AI can accurately adopt my style and make my work easier by formulating emails. Take into account: - general tone (friendly, direct, formal, collegial), - typical length and content structure, - frequently used words, phrases and phrases, - technical depth, - concrete examples of greetings, introductions, main parts and conclusions.

Step 2: Additionally, research typical elements that make emails sound "AI-like." Result: Then create a set **Custom Instructions for Microsoft Copilot in Outlook** **in English**, formatted **as a Code Interpreter Element in Markdown**. Include in it: - general instructions to make emails sound as human and natural as possible,

What this means for your workday

Everything you need is in this article. If you want to fit it to your own setup, 1:1 coaching is the place to start.