MCP Server for Multiple Outlook Accounts

A local, single-connector Model Context Protocol server that lets an AI assistant operate several Outlook / Microsoft 365 mailboxes at once — searching, reading, drafting, sending, and organising mail — through one safety-annotated tool surface, with OAuth tokens that never leave your machine.

This is the Outlook / Microsoft Graph provider variant of a provider-neutral specification.

• 📄 doc/business-specification.md — provider-neutral business + functional spec (the contract).

• 🔌 doc/provider-mapping.md — how neutral requirements bind to Microsoft Graph.

• 🏗️ doc/architecture.md — how this variant is designed and built.

• ✅ doc/traceability-matrix.md — every requirement → module → test.

• 🚀 doc/ONBOARDING.md — operator guide: register an Entra app, handle consent, connect a mailbox.

• ✅ doc/LIVE-ACCEPTANCE.md — live acceptance runbook + npm run live-smoke (the remaining work).

• 🤝 doc/CONTRIBUTING.md — handoff guide: how we work, workflow, and the per-phase record.

• 📋 doc/HANDOVER.md — handover snapshot: what's done and the outstanding-work checklist.

Project status: feature-complete (offline build)

Built with TypeScript 6.0.3; build, typecheck, tests (179), and format all green. All eight capabilities are implemented and the offline build is feature-complete. What exists today:

• ✅ Architecture design + requirements traceability matrix (doc/).

• ✅ Auth core: Entra credential-source discovery, MSAL public-client (consent + silent refresh), secure token store (0600/0700, atomic + cross-process-locked), account-selection registry.

• ✅ Account-management CLI: outlook-mcp-auth connect | list | remove.

• ✅ Microsoft Graph client: thin fetch wrapper with a per-request timeout, bounded jittered retry (with the no-duplicate-send policy), and actionable error mapping.

• ✅ Read tools: list_accounts (C1), search_conversations (C2), read_conversation (C3) — with Gmail-style search-operator translation and bounded, truncating output.

• ✅ Write tools: create_draft (C4) and send_message (C5) — recipient parsing (Display Name <addr>), header-injection stripping, allow-listed/TOCTOU-safe attachments, local outgoing-size validation, and reply threading. Small attachments ride inline; large ones (> ~3 MB) upload to the draft via a Graph upload session, so send becomes create-draft → upload → send with the final /send under the nonDuplicable retry policy — a retry can never double-deliver.

• ✅ Organise tools: list_labels (C6), create_label (C7), and organize_mail (C8) — the label-decomposition fan-out that maps one neutral organise request to the right mix of Graph category-PATCH / read-state / move calls (archive, trash, junk — mutually exclusive), applied per message across a conversation under a bounded concurrency limit, reporting the union of resulting labels. list_labels enumerates folders recursively (full paths).

• ✅ Hardening + onboarding: a secret-redaction boundary so tokens/credentials can never reach the logs (NFR-SEC-6), and the operator onboarding guide (Entra app registration, unverified-app consent, the connect CLI).

Remaining: the live acceptance runs (real browser consent + real Graph calls) that the operator performs against an Entra app registration + Outlook mailbox. See doc/architecture.md §13.

Tests mock Microsoft Graph and MSAL. Live §13 acceptance — real browser consent and Graph calls — requires an Entra app registration + Outlook mailboxes and is run locally by the operator.

Related MCP server: m365-mcp-server

Capabilities (spec §5)

Plus an out-of-band account-management CLI (outlook-mcp-auth connect | list | remove).

Development

Requires Node.js ≥ 18 (developed on Node 22).

npm install
npm run typecheck      # tsc --noEmit
npm run build          # compile to dist/
npm test               # vitest (Graph/MSAL mocked)
npm run format:check   # prettier

Configuration

All operational knobs are environment variables (see .env.example):

Connecting a mailbox

For the full walkthrough — Entra app registration, the unverified-app consent policy, and troubleshooting — see doc/ONBOARDING.md. The short version:

1. Register a public-client app in Entra ID with the redirect URI http://localhost and the delegated scopes Mail.ReadWrite, Mail.Send, User.Read, offline_access.

2. Drop a credentials*.json into the data dir (or point OUTLOOK_OAUTH_CREDENTIALS at it):

   { "clientId": "<application-client-id>", "tenant": "common" }

   Multiple credentials*.json files are auto-discovered, so accounts under different app registrations each refresh with the client that authorised them.

3. Connect, list, and remove mailboxes:

   outlook-mcp-auth connect            # opens the browser for consent
   outlook-mcp-auth connect --source acme   # pick a specific app registration
   outlook-mcp-auth list
   outlook-mcp-auth remove user@example.com

Security posture

OAuth tokens are stored only on the local machine (file mode 600 in a 700 data dir). Reading local files by path for attachments is disabled by default and only allowed from an explicit allow-list. The server never logs tokens, credentials, or message content. See doc/architecture.md §9.

License

MIT — see LICENSE.