notmuchproxy

Give an LLM read-only access to your email.

notmuchproxy is a small API server over a notmuch email archive. It exposes the same four tools two ways:

• an OpenAPI/REST API (schema at /openapi.json), usable as an Open WebUI tool server

• an MCP endpoint (streamable HTTP at /mcp/), usable from Claude Code, claude.ai, and any other MCP client

There is no UI and no write path: the server only ever reads the archive, so the worst an over-eager LLM can do is search your email too enthusiastically.

The tools

Plus an unauthenticated GET /healthz. Everything else requires Authorization: Bearer $NOTMUCHPROXY_API_KEY — including the MCP endpoint. The MCP tools are derived from the OpenAPI schema at startup, so the two surfaces can't drift apart.

Search queries are validated before they reach xapian. Unknown prefixes (status:unread), capitalized prefixes (From:alice), and nonexistent tags (tag:handled) would otherwise silently match nothing — to xapian they are just terms no message contains — so a mistyped query looks exactly like an empty mailbox. The proxy instead rejects them with a 400 naming the problem and suggesting the fix (for unread mail use tag:unread; Tags in this archive: ...), which is the kind of feedback LLM callers actually act on. docs/email-assistant-knowledge.md has a system-prompt blurb teaching small models to use the tools well.

Related MCP server: Email MCP Server

Configuration

Everything is environment variables:

Authentication

Pick exactly one mechanism (the server refuses to start with both or neither); it applies to both the REST API and the MCP endpoint.

Static bearer token — simplest; what Open WebUI's OpenAPI tool servers and Claude Code's --header flag speak. claude.ai custom connectors can not use this mode (they only support OAuth).

OIDC via an external identity provider — works with any OIDC IdP (authentik, Keycloak, Google, ...). notmuchproxy presents a spec-compliant MCP authorization server to clients — including the dynamic client registration claude.ai requires — while acting as an ordinary OIDC client of your IdP upstream (your IdP does not need to support DCR itself). Tokens issued through the flow are accepted on both the MCP and REST endpoints.

IdP setup (authentik example): create an OAuth2/OpenID provider with a confidential client and redirect URI $NOTMUCHPROXY_PUBLIC_URL/auth/callback, scopes openid profile email. Who may authorize is controlled by your IdP's own policies (in authentik, bind the application to users/groups).

¹ optional if the host has a notmuch config that already points at the database.

Running in production

The server is distributed as a docker image. Mount your maildir — which must already contain the .notmuch index — read-only at /mail:

docker run -d -p 8000:8000 \
  -e NOTMUCHPROXY_API_KEY=some-long-random-string \
  -v /path/to/your/mail:/mail:ro \
  ghcr.io/igor47/notmuchproxy:latest

Indexing (notmuch new) is not done by this container — keep running it wherever your mail is delivered. The container picks up index updates automatically since xapian readers don't block writers.

docker compose, as a non-root user

The image runs as a built-in non-root user (uid 1000) by default. If your maildir is owned by a different user, override user: so the container can read the mount — no rebuild needed:

services:
  notmuchproxy:
    image: ghcr.io/igor47/notmuchproxy:latest
    restart: unless-stopped
    # run as the uid/gid that owns your maildir (`id -u`/`id -g`);
    # omit entirely if uid 1000 can read your mail
    user: "1000:1000"
    ports:
      - "8000:8000"
    environment:
      NOTMUCHPROXY_API_KEY: ${NOTMUCHPROXY_API_KEY:?set this in .env}
    volumes:
      - /path/to/your/mail:/mail:ro

The app never writes to the archive (and the :ro mount enforces that), so read permission on the maildir is all it needs.

Connecting clients

Open WebUI

In static mode, add an OpenAPI tool server (Admin Settings → Tools):

• URL: http://your-host:8000

• Auth: Bearer, key = your NOTMUCHPROXY_API_KEY

Open WebUI fetches /openapi.json (which is unauthenticated, like /healthz) to discover the tools, then sends the bearer token on each call.

In OIDC mode, use Open WebUI's MCP tool server type instead, pointed at https://your-host/mcp with OAuth 2.1 auth — it performs the same discovery and login flow as claude.ai.

Tool servers added under Admin Settings are called from the Open WebUI backend, but ones added in a user's own Settings → Tools are called directly from the browser — that path needs CORS, which is enabled for all origins by default (lock it down with NOTMUCHPROXY_CORS_ORIGINS=https://your-webui-host).

claude.ai (OIDC mode only)

Settings → Connectors → Add custom connector, URL https://your-host/mcp. Claude discovers the OAuth endpoints, registers itself dynamically, and sends you through your IdP's login/consent in the browser. No client id/secret needs to be entered on the claude.ai side.

Claude Code

Static mode:

claude mcp add --transport http notmuch http://your-host:8000/mcp \
  --header "Authorization: Bearer $NOTMUCHPROXY_API_KEY"

OIDC mode — omit the header; Claude Code runs the OAuth flow in your browser:

claude mcp add --transport http notmuch https://your-host/mcp

Other MCP clients

Any client that speaks streamable HTTP can connect to http://your-host:8000/mcp, authenticating with the static bearer token or the OAuth flow depending on the server's configured mode.

Development

Tooling is managed by mise; the notmuch CLI must be on your PATH (it's in every distro's repos).

mise install        # python + uv
mise run install    # create venv, sync deps
mise run test       # run the test suite (builds a throwaway notmuch archive)
mise run check      # ruff lint + format check + pyright (CI mode)
mise run check:fix  # same, but auto-fix what's fixable
mise run dev        # serve on :8000 against generated fixtures (key: dev-key)

Other tasks: mise run fixtures (regenerate the local dev archive), mise run docker:build, mise run docker:test (run the suite inside docker), mise run docker:run. See mise tasks for the full list.

CI runs the same mise tasks, then runs the suite again inside the docker image (against Debian's notmuch rather than the host's) before pushing to ghcr.io/igor47/notmuchproxy on pushes to main and v* tags.

Architecture notes

• notmuch access: shells out to the notmuch CLI using --format=json output, via a thin wrapper in src/notmuchproxy/notmuch.py. No Python bindings, so there is no libnotmuch version-matching to worry about; the database path is passed via the NOTMUCH_DATABASE environment variable.

• one definition, two protocols: the FastAPI routes are the source of truth; fastmcp's FastMCP.from_fastapi() converts the OpenAPI schema into MCP tools at startup and dispatches tool calls to the routes in-process.

• bodies: text/plain parts are preferred; HTML-only messages get a naive tag-stripped rendering. Attachments are listed by filename but not served.

• fixtures: python -m notmuchproxy.fixtures <dir> generates a small synthetic maildir + notmuch index, used by the tests and mise run dev.

License

MIT