OutlookAI — Free Open-Source Outlook AI Add-in

⚠️ Still in active development. Chat, Inbox Copilot, Inbox Reports, and Excel/PDF exports are live on the feature/codex-oauth-migration branch and are being merged to master. Track the current state in the open pull requests.

The free open-source alternative to GPT for Outlook, Mailbutler, Lavender, Compose AI, OtterMail, Boomerang Respondable, Mailmaestro, EmailTree, SaneBox AI, and Spike Magic AI — running inside Microsoft Outlook desktop and billed against your own ChatGPT subscription. No per-seat fee, no proxy server, no data sent through a third party.

TL;DR

OutlookAI is a free, open-source Outlook AI add-in that replaces the paid "AI for Outlook" market. Sign in once with your own ChatGPT Plus or Pro account; OutlookAI runs entirely inside your Outlook process — no proxy, no SaaS middleware, no telemetry. You get:

Chat in the compose pane: WebView2 surface with streaming, multi-round tool dispatch, model + reasoning-effort picker.
Inbox Copilot taskpane: selection-aware actions, full multi-round chat over the messages you highlighted.
Inbox Reports taskpane: templated chips that turn your inbox into markdown reports, action items, vendor breakdowns.
Excel and PDF exports: model-callable export tools plus a per-message Save as PDF button. Files land in Documents\OutlookAI\Reports\ with Open / Show in folder.
15 Outlook tools the model can call (11 always on + 4 admin-gated safe writes; no send / delete / move tools by design).
Voice transcription from the same ChatGPT credential.
Open source under MIT, fork-friendly, auditable end-to-end.

What you get

💬 Chat tab (in compose pane)

WebView2-based chat that lives next to the draft you are writing. Streaming text, multi-round tool dispatch with visible tool cards, cancellation that preserves partial text, and light / dark / high-contrast themes. Per-turn reasoning-effort override. Clear, copy-to-clipboard, and Save-as-PDF buttons on every assistant message.

📥 Inbox Copilot (taskpane)

Open the AI Assistant taskpane on any Outlook explorer window and the same chat surface attaches to your inbox. Highlighting one or more messages feeds them into the context. Quick-action chips for common workflows ("summarize this thread", "draft a reply") and full freeform chat with the entire 15-tool mailbox surface.

📊 Inbox Reports (taskpane)

A second taskpane focused on generating reports from your mailbox. Six default templated chips (action items, top senders, out-of-office digest, project status, conversations with a specific person, stats by sender). Each chip prompts the model with a structured intent and renders the markdown response inline. Save the report as PDF, or export underlying data as Excel.

📑 Excel and PDF exports

Two model-callable export tools:

outlook_export_excel produces a styled .xlsx with bold/frozen header row, autofilter, and per-column formatting (text / number / currency / date / datetime / boolean) via ClosedXML.
outlook_export_pdf renders polished markdown through an isolated off-screen WebView2 instance into A4 PDF with header bar and no chat-UI chrome.

Both save to ~\Documents\OutlookAI\Reports\ with auto-generated, timestamped, collision-safe filenames. Tool results surface as inline file cards with Open and Show in folder buttons. Every file action goes through a path-policy gate that rejects any path outside the Reports directory.

📎 Per-message Save as PDF

Every assistant message gets a small button that exports just that message — the markdown the chat is showing, not the rendered HTML — to PDF. One click, no model round-trip.

🛠 15 model-callable Outlook tools

Always on (11):

outlook_get_current_compose_state
outlook_get_current_selection
outlook_list_folders
outlook_search_messages
outlook_read_message
outlook_read_messages (bulk)
outlook_count_messages
outlook_aggregate_messages (group + top-N)
outlook_list_recent_threads_with
outlook_export_excel
outlook_export_pdf

Admin-gated safe writes (4):

outlook_create_draft
outlook_mark_as_read
outlook_flag_message
outlook_set_category

By design there is no send, delete, move-to-deleted, or permanent-mutation tool. The admin password gates which write tools, if any, the model can call.

🎙 Voice

The mic button opens a Realtime WebSocket at wss://api.openai.com/v1/realtime?model=gpt-realtime-1.5 using the same OAuth token. Transcription lands back in the prompt textbox. No separate Whisper API key.

⚙️ Settings

The gear icon opens a password-gated Settings dialog with:

ChatGPT account: Sign In / Sign Out / Refresh.
Model picker: 7 options (gpt-5.5, gpt-5.5-pro, gpt-5.4, gpt-5.4-mini, gpt-4.1-mini, gpt-4.1-nano, gpt-5.3-codex).
Reasoning effort dropdown, filtered per model.
4 checkboxes for the safe-write tools (each can be individually enabled).
Admin password rotation.

Per-user settings persist to %APPDATA%\OutlookAI\config.xml.

How it compares

Feature	OutlookAI	GPT for Outlook	Mailbutler	Lavender	OtterMail	Compose AI	Boomerang Respondable	Mailmaestro	EmailTree	SaneBox AI
Price	$0 (BYO ChatGPT sub)	$7-$15/user/mo	$9.95-$32.95/mo	$29-$89/mo	$10-$20/mo	$9.99-$29/mo	$4.99-$22.99/mo	$19-$39/mo	enterprise (POA)	$7-$36/mo
Source code	MIT, public	closed	closed	closed	closed	closed	closed	closed	closed	closed
OAuth via your own ChatGPT sub	yes	no	no	no	no	no	no	no	no	no
Tool calling on real mailbox data	15 tools	partial	partial	no	partial	no	no	no	yes (proprietary)	partial
Runs entirely in-process (no proxy)	yes	no	no	no	no	no	no	no	no	no
Inbox Copilot taskpane	yes	no	no	no	no	no	no	partial	partial	no
Inbox Reports + Excel/PDF export	yes	no	no	no	no	no	no	no	partial	no
Save any chat output as PDF	yes	no	no	no	no	no	no	no	no	no
Voice (speech-to-text)	yes	yes	partial	no	yes	no	no	no	no	no
Per-tool write permissions	yes	no	no	no	no	no	no	no	no	no
Telemetry / data leaves your machine	none	yes	yes	yes	yes	yes	yes	yes	yes	yes
Outlook desktop (VSTO)	yes	yes	yes	partial	yes	no	partial	partial	yes	partial
Auditable code	yes	no	no	no	no	no	no	no	no	no

Public list prices as of writing (May 2026), rounded for readability. The paid alternatives charge per user per month. OutlookAI is free and bills inference against your existing ChatGPT subscription.

Why OutlookAI

Bring your own ChatGPT subscription — no extra monthly fee. OutlookAI uses the OAuth flow Codex CLI uses (client_id app_EMoamEEZ73f0CkXaXp7hrann), so signing in with your ChatGPT account is enough. There is no second OpenAI API key to manage and no vendor middleman charging a per-seat license.
Runs entirely in your Outlook process. No proxy server sees your mail or your OAuth token. Every paid Outlook AI add-in we know of routes either your email content, your API key, or both through their own servers. OutlookAI talks directly to chatgpt.com/backend-api/codex/responses (text) and wss://api.openai.com/v1/realtime (voice) from inside Outlook.exe.
Real tools, real reports, real exports. Not just "rewrite this email." The model can search your mailbox, summarize threads, aggregate by sender or day, draft replies, and export the results to Excel or PDF — all from inside the chat window, with explicit tool cards so you can see every read.
Open source under MIT. Read the code, fork it, audit the security model, contribute. The competitors are black boxes.

Install

For a single workstation:

# 1. Clone the repo or download the latest Release zip
git clone https://github.com/kirklandsig/OutlookAI.git
cd OutlookAI

# 2. (Optional) Refresh the vendored WebView2 bootstrapper
.\Deploy\Fetch-WebView2Bootstrapper.ps1

# 3. Publish Release
& "C:\Program Files\Microsoft Visual Studio\18\Community\MSBuild\Current\Bin\MSBuild.exe" `
  "VSTO2\OutlookAI.sln" /target:Publish /p:Configuration=Release /p:Platform="Any CPU" `
  /p:PublishDir="C:\OutlookAI\"

# 4. Install (elevated)
Set-ExecutionPolicy -Scope LocalMachine -ExecutionPolicy RemoteSigned
.\Deploy\Install-OutlookAI.ps1 -SourcePath "C:\OutlookAI"

# 5. Open Outlook → AI Assistant → sign in with your ChatGPT account.

For multi-user RDS / Terminal Server installs and IT-managed images, see Deploy/README.txt (and the short docs/Install.md summary).

Architecture

Outlook.exe
  └── AITaskPane (WinForms tab control)
        ├── Chat                  → ChatController → CodexChatService → OpenAI Codex Responses API
        ├── Inbox Copilot         → InboxCopilotController → CodexChatService → tool catalog
        └── Inbox Reports         → InboxReportsController → CodexChatService → tool catalog

CodexChatService
  └── OutlookToolHost / ToolDispatcher
        └── 15 IOutlookTool implementations
              ├── LiveOutlookSurface (Outlook COM)
              └── Services/Export
                    ├── ExcelWorkbookBuilder       (ClosedXML)
                    ├── PdfRenderer                (off-screen WebView2 + PrintToPdfAsync)
                    └── PrintTemplateRenderer

ExportBridge (WebMessageReceived)
  ├── export_pdf
  ├── open_file              ← path policy
  └── reveal_in_explorer     ← path policy

Key components:

Services/CodexChatService.cs — Codex Responses request/streaming, multi-round tool dispatch, parallel tool calls, cancellation.
Services/Tools/OutlookToolHost.cs — tool catalog construction and per-tool admin-write gating.
Services/Tools/LiveOutlookSurface.cs — Outlook COM surface for read/write/search; AdvancedSearch + iterative-folder fallback; budgeted / early-stop scan policy.
Services/Export/ExcelWorkbookBuilder.cs, Services/Export/ExcelCellCoercer.cs — ClosedXML Excel construction.
Services/Export/PdfRenderer.cs, Services/Export/PrintTemplateRenderer.cs — off-screen WebView2 PDF rendering with an isolated user-data folder.
TaskPane/Chat/ExportBridge.cs — WebView2 host-message bridge for export_pdf / open_file / reveal_in_explorer, guarded by IExportPathPolicy.
WebUI/* — chat.js, markdown.js, styles.css, print-template.html, print-styles.css. Extracted from chat.js so the same markdown renderer drives chat and PDF.

Security model

OAuth via ChatGPT. Tokens stored at:
- C:\ProgramData\OutlookAI\auth.json (machine, RDS-shared by design).
- %APPDATA%\OutlookAI\config.xml (per-user settings).
No telemetry. Outbound traffic is exactly two endpoints from inside Outlook.exe:
- https://chatgpt.com/backend-api/codex/responses (text inference).
- wss://api.openai.com/v1/realtime (voice transcription).
Path policy on file actions. IExportPathPolicy.RequireInsideReportsDir(...) rejects any open/reveal path that escapes Documents\OutlookAI\Reports\. Path traversal attempts are logged and never launched.
No destructive tools. No outlook_send_message, outlook_delete_message, or outlook_move_to_deleted. The admin can additionally disable any safe-write tool from Settings.
RDS shared-credential. On multi-user servers, auth.json grants Authenticated Users: Modify — explicit accepted risk. Rotation procedure is documented in Deploy/README.txt.

FAQ

Is there a free alternative to GPT for Outlook?

Yes — OutlookAI. It is open-source under MIT, free to use, and bills inference against your existing ChatGPT Plus or Pro subscription instead of charging a separate per-seat fee.

Can I use my ChatGPT Plus subscription inside Outlook?

Yes. OutlookAI uses the same OAuth client ID Codex CLI uses, so signing in with your ChatGPT account is enough. There is no second OpenAI API key to manage.

How does OutlookAI compare to Mailbutler / Lavender / Compose AI?

Mailbutler bundles AI drafting with snooze, send-later, tracking, and other email-productivity features that route data through their servers. Lavender focuses on tone scoring and predictive suggestions during typing. Compose AI is a browser autocomplete. OutlookAI is a native VSTO add-in with multi-round chat, taskpane Copilot, taskpane Reports, and Excel/PDF exports — different design point, broader capability surface, $0 vs $5-$89/mo.

Does OutlookAI work with Outlook Web (OWA) or Outlook for Mac?

Not yet. OutlookAI is a VSTO add-in for Outlook desktop on Windows (Outlook 2016, 2019, 2021, 2024, and Microsoft 365). OWA and Outlook for Mac would require a separate Office.js add-in; that is on the long-term roadmap.

What model does it use?

Default gpt-5.5 for text and gpt-realtime-1.5 for voice. Admin can change the model from Settings.

Where does my data go?

Two endpoints, both directly from Outlook.exe. No third-party proxy, no telemetry, no analytics. See the Security model section above.

Does it work on Windows Server / RDS?

Yes — that is the primary deployment target. See Deploy/README.txt.

How do I uninstall?

.\Deploy\Uninstall-OutlookAI.ps1

Removes the add-in registration, the install folder, and the local OAuth artifacts. The Backups/ subfolder is preserved.

Status and roadmap

Shipped on feature/codex-oauth-migration (merging to master now):

Chat tab in compose pane.
Inbox Copilot taskpane.
Inbox Reports taskpane with six templated chips.
Excel export tool with typed columns and per-column formatting.
PDF export tool with off-screen WebView2 renderer.
Per-message Save as PDF in chat and reports.
File cards with Open / Show in folder, guarded by path policy.
OAuth via ChatGPT (no API keys to manage).
Voice transcription via OpenAI Realtime.
RDS / Terminal Server install path.

Known gaps / explicit follow-ups:

Multi-sheet Excel workbooks.
PDF page numbers, footer, table of contents, embedded images.
Settings UI for picking a custom Reports folder.
CSV, .docx, and other export formats.
Mac / OWA support (would require an Office.js add-in).

Contributing

# Clone and restore
git clone https://github.com/kirklandsig/OutlookAI.git
cd OutlookAI

# Build (Debug)
& "C:\Program Files\Microsoft Visual Studio\18\Community\MSBuild\Current\Bin\MSBuild.exe" `
  "VSTO2\OutlookAI.sln" /p:Configuration=Debug /p:Platform="Any CPU"

# Test (current branch: 546/546 passing)
& "C:\Program Files\Microsoft Visual Studio\18\Community\Common7\IDE\CommonExtensions\Microsoft\TestWindow\vstest.console.exe" `
  "VSTO2\OutlookAI.Tests\bin\Debug\net472\OutlookAI.Tests.dll"

Branch model:

master — released code.
feature/<feature-name> — feature branches with their own spec under docs/superpowers/specs/ and plan under docs/superpowers/plans/.

Spec / plan workflow: see docs/superpowers/ for the spec → plan → implementation cycle that drove every phase of OutlookAI development.

Requirements

Windows 10 / 11, or Windows Server 2019 / 2022 / 2025.
Microsoft Outlook 2016 / 2019 / 2021 / 2024 / Microsoft 365 (desktop).
.NET Framework 4.7.2.
Visual Studio Tools for Office Runtime.
Microsoft Edge WebView2 Evergreen Runtime (installed by Install-OutlookAI.ps1 if missing).

License

MIT — see LICENSE.

Name		Name	Last commit message	Last commit date
Latest commit History 211 Commits
.github/workflows		.github/workflows
Deploy		Deploy
VSTO2		VSTO2
docs		docs
.gitignore		.gitignore
CLAUDE.md		CLAUDE.md
LICENSE		LICENSE
README.md		README.md

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OutlookAI — Free Open-Source Outlook AI Add-in

TL;DR

What you get

💬 Chat tab (in compose pane)

📥 Inbox Copilot (taskpane)

📊 Inbox Reports (taskpane)

📑 Excel and PDF exports

📎 Per-message Save as PDF

🛠 15 model-callable Outlook tools

🎙 Voice

⚙️ Settings

How it compares

Why OutlookAI

Install

Architecture

Security model

FAQ

Is there a free alternative to GPT for Outlook?

Can I use my ChatGPT Plus subscription inside Outlook?

How does OutlookAI compare to Mailbutler / Lavender / Compose AI?

Does OutlookAI work with Outlook Web (OWA) or Outlook for Mac?

What model does it use?

Where does my data go?

Does it work on Windows Server / RDS?

How do I uninstall?

Status and roadmap

Contributing

Requirements

License

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