claude-mail-mcp

Self-hosted IMAP / SMTP / CalDAV connector for Claude with multi-account support. A Streamable HTTP MCP server that lets Claude.ai read and write your email + calendar against any RFC-compliant mailbox.

Built because every other Claude email connector targets Gmail. This one is for the rest of us — Mailbox.org, Fastmail, iCloud, Mailcow, iRedMail, Migadu, Nextcloud, your own Postfix box. If your provider speaks IMAP, SMTP and CalDAV, this works. One connector, all your inboxes.

What it does

Exposes 14 MCP tools to Claude:

Accounts (1)

Mail (9)

Calendar (4)

Every tool accepts an optional account: "<id>" parameter to pick a mailbox; omit it to use the default account. So "list unread in INBOX of work account" vs "compare today's calendar across work and personal" both work in one connector.

Related MCP server: IMAP MCP Server

Why bring-your-own-server?

Hosted email-AI services need full mailbox access. That's a lot of trust to hand to a vendor. This connector flips the model: you run it, you hold the credentials, no third party between Claude and your inbox.

• One Node process per mailbox

• Credentials in a single .env file

• One Bearer token gates every MCP call

• Add the URL to Claude.ai once, done

Quick start

git clone https://github.com/maxx3250/claude-mail-mcp.git
cd claude-mail-mcp
npm install
cp .env.example .env
# Generate an AUTH_TOKEN and fill it into .env:
#   echo "AUTH_TOKEN=$(openssl rand -hex 32)" >> .env
npm run build
npm start

The server boots with no mailboxes configured — that's fine. Add them via the OAuth shim's /settings UI (see Deployment) or hand-craft an accounts.json:

{
  "version": 1,
  "accounts": [
    {
      "id": "main",
      "label": "Main",
      "default": true,
      "imap": { "host": "imap.mailbox.org", "port": 993, "user": "you@example.com", "pass": "secret", "tls": true },
      "smtp": { "host": "smtp.mailbox.org", "port": 465, "user": "you@example.com", "pass": "secret", "tls": true },
      "mail": { "defaultFrom": "you@example.com", "draftsFolder": "Drafts", "sentFolder": "Sent" }
    }
  ]
}

Save as /root/.config/mail-mcp/accounts.json (chmod 600), or set ACCOUNTS_FILE=./accounts.json in .env for local dev. The backend re-reads via fs.watch, no restart needed.

Smoke test:

curl http://localhost:3220/health
# {"status":"ok","server":"claude-mail-mcp","version":"0.2.0","accounts":[{…}],…}

Connecting from Claude.ai

The server speaks the Streamable HTTP MCP transport. To use it from Claude.ai (web), you need an OAuth 2.1 + DCR + PKCE layer in front because Claude.ai does not support raw Bearer auth.

The recommended setup mirrors what claude-meta-mcp uses:

1. Terminate TLS with nginx / Caddy on a public hostname (e.g. mcp-mail.yourdomain.com)

2. Put a tiny OAuth shim in front that issues short-lived Bearer tokens after a basic-auth login

3. Add the public URL as a Custom Connector in Claude.ai (Settings → Connectors → Add custom)

See docs/DEPLOYMENT.md for the full nginx + systemd + shim recipe.

For local testing without a shim, you can call /mcp directly with Authorization: Bearer <AUTH_TOKEN> from any MCP client that supports custom headers (Claude Desktop config, or a stdio bridge).

Provider notes

App passwords (mandatory on 2FA accounts)

CalDAV endpoints

If your provider doesn't speak CalDAV, leave CALDAV_URL empty and the calendar tools won't be registered. Mail still works.

Architecture

Claude.ai (web)
    │  HTTPS + OAuth 2.1
    ▼
nginx (TLS, /health passthrough)
    │
    ├──▶ /mcp/* ─▶ OAuth shim (Port 3212)  ──▶ Bearer ──▶ this server (Port 3220)
    └──▶ /health ────────────────────────────────────────▶ this server (Port 3220)

this server
    ├── ImapClient   ──▶  imapflow  ──▶  IMAP server (993/143)
    ├── SmtpClient   ──▶  nodemailer ─▶  SMTP server (465/587)
    └── CalDavClient ──▶  tsdav     ──▶  CalDAV server

Everything is one Node process. IMAP holds a single long-lived connection with per-call mailbox locks. SMTP and CalDAV are stateless per call.

Security model

See SECURITY.md for the threat model and docs/HARDENING.md for the full operator checklist.

Defaults in one sentence: TLS via Let's Encrypt + HSTS + rate-limited htpasswd + OAuth 2.1 with CSRF guard + non-root systemd unit with ProtectSystem=strict + kernel-level loopback-only filter + credentials chmod 600 owned by a dedicated mailmcp user.

Quick summary

• Transport: TLS 1.3 (Let's Encrypt, auto-renew), HSTS, X-Frame-Options: DENY, X-Content-Type-Options: nosniff, Referrer-Policy: no-referrer, X-Robots-Tag: noindex.

• Auth: OAuth 2.1 + DCR + PKCE + JWT (RS256, 1h access, 30d refresh) gated by htpasswd login. CSRF guard on /settings POST. Brute-force throttled at nginx (10 req/min on auth endpoints).

• Process: Both services run as a dedicated non-root mailmcp system user (no shell). Full systemd hardening: NoNewPrivileges, ProtectSystem=strict, ProtectHome, ProtectKernel*, ProtectClock, ProtectHostname, ProtectProc=invisible, RestrictNamespaces, LockPersonality, SystemCallFilter=@system-service ~@privileged @resources, MemoryMax=512M.

• Network: Backend + shim bound to 127.0.0.1 only. Shim also blocks non-loopback at kernel level (IPAddressDeny=any). UFW default-deny on the host.

• Storage: Credentials chmod 600, owned by mailmcp, in /var/lib/mail-mcp/. htpasswd file chmod 640 (not world-readable). .env chmod 640 root:mailmcp.

• Output: list_accounts returns id/label/From — never credentials. Logs never include passwords or Bearer tokens.

• Destructive tools (delete_message) document irreversibility so Claude.ai surfaces a confirmation step. Prefer move_message to a Trash folder for reversibility.

Full threat-model walkthrough and operator hardening checklist in docs/HARDENING.md. Reporting issues: see SECURITY.md.

Roadmap

• v0.2 ✅ — Multi-account per deployment, browser setup flow (this release)

• v0.3 — Threading-aware list_threads tool, attachment download as base64, calendar invitation (iMIP) sending

• v0.4 — CardDAV (contacts), JMAP support as an alternative to IMAP for Fastmail/Topicbox

• v1.0 — Audit log, Prometheus metrics, rate limiting, hardened deployment guide

License

MIT — see LICENSE.

Acknowledgements

• imapflow — modern Promise-based IMAP client

• nodemailer — the only Node SMTP client worth using

• tsdav — clean TypeScript WebDAV/CalDAV/CardDAV

• ical.js — battle-tested iCalendar parser

• @modelcontextprotocol/sdk — Anthropic's official MCP SDK

Built by Markus Stöger — WooCommerce, headless commerce and AI integration.