OutlookAI

An AI-powered email writing assistant for Microsoft Outlook, built as a VSTO add-in.

What's New (April 2026)

• Updated AI models - Now uses Claude Opus 4.6 (writing) and GPT-4o Transcribe (voice)
• Global config file - Admins can set API keys and models via C:\Program Files\OutlookAI\config.xml without rebuilding
• Server 2025 fix - Fixed invisible button text on Windows Server 2025
• Resiliency protection - Outlook can no longer auto-disable the add-in
• Better error messages - API errors now show in a full dialog instead of a truncated label

Features

• Quick Actions - One-click buttons to improve your email drafts:

  • Proofread (grammar, spelling, punctuation)
  • Revise (clarity and flow)
  • Shorten / Lengthen
  • Formal / Friendly tone

• Draft New Emails - Describe what you want to write and let AI generate the email

  • Voice input support using OpenAI Whisper
  • Context-aware replies (AI sees the email chain)

• Insert or Replace - Choose to add content at the top (preserving email chain) or replace everything

Requirements

• Windows 10/11 or Windows Server 2019/2022/2025
• Microsoft Outlook 2016, 2019, 2021, or 2024 (desktop version)
• .NET Framework 4.8
• Visual Studio Tools for Office Runtime

API Keys Required

This add-in requires:

• Anthropic API Key (Claude) - Required for all AI features. Get one at console.anthropic.com
• OpenAI API Key (Whisper) - Optional, for voice input. Get one at platform.openai.com

Installation

Option 1: Pre-configured Build (Enterprise/RDS)

1. Build the solution in Release mode
2. Publish from Visual Studio (Right-click project > Publish)
3. Copy the publish folder to your deployment location
4. Run Deploy\Install-OutlookAI.ps1 as Administrator:

Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope LocalMachine
Unblock-File -Path "C:\OutlookAI\Install-OutlookAI.ps1"
cd C:\OutlookAI
.\Install-OutlookAI.ps1 -SourcePath "C:\OutlookAI"

6. Edit C:\Program Files\OutlookAI\config.xml to set your API keys and model preferences

Option 2: Per-User Install

1. Build and publish the solution
2. Run setup.exe from the publish folder
3. Open Outlook and configure API keys in the Settings panel

Usage

1. Open Outlook and compose a new email (New, Reply, or Forward)
2. Click the AI Assistant button in the ribbon
3. The task pane opens on the right side

Quick Actions

• Write your email draft first
• Click any Quick Action button (Proofread, Revise, etc.)
• Review the result and click Insert or Replace

Draft New Email

• Type or speak your instructions (e.g., "Write a thank you email to John for the meeting")
• Click Draft Email
• Review and insert the result

Voice Input

• Click the red circle button to start recording
• Speak your instructions
• Click again to stop and transcribe
• Requires OpenAI API key

Building from Source

Prerequisites

• Visual Studio 2022
• Office/SharePoint development workload
• .NET desktop development workload

Build Steps

1. Clone this repository
2. Open VSTO2\OutlookAI\OutlookAI.sln
3. Restore NuGet packages
4. Build > Rebuild Solution

Configuration

Settings are loaded in this order (each overrides the previous):

1. Hardcoded defaults in the compiled DLL
2. Global config - C:\Program Files\OutlookAI\config.xml (admin-managed, applies to all users)
3. Per-user config - %APPDATA%\OutlookAI\config.xml (created when a user saves settings)

The install script creates a default global config. Edit it to set API keys and models for all users without rebuilding.

Access the Settings panel by clicking the gear icon in the add-in. The default admin password is admin.

Deployment Scripts

Located in the Deploy folder:

• Install-OutlookAI.ps1 - Per-machine install for all users (RDS/Terminal Server)
• Uninstall-OutlookAI.ps1 - Remove the add-in
• Enable-OutlookAI-User.ps1 - Re-enable if Outlook disabled the add-in

Troubleshooting

Add-in doesn't appear

• Restart Outlook
• Check File > Options > Add-ins
• Run Enable-OutlookAI-User.ps1

Add-in keeps getting disabled

• Outlook's "Resiliency" feature may disable slow-loading add-ins
• Run Enable-OutlookAI-User.ps1 - this now sets a Group Policy key to permanently prevent disabling
• Add to logon scripts for automatic protection

"Untrusted" or security errors

• Ensure all files are unblocked (Right-click > Properties > Unblock)
• Or run: Get-ChildItem -Path "C:\Program Files\OutlookAI" -Recurse | Unblock-File

API errors

• Verify your API keys are correct
• Check your API account has credits/quota
• Ensure TLS 1.2 is enabled (default on modern Windows)

License

MIT License - See LICENSE file

Acknowledgments

• Anthropic Claude API - AI text generation
• OpenAI Whisper API - Speech-to-text
• NAudio - Audio recording