Multi-Account Gmail

gmail-mcp

[Python] [License: MIT] [tests: 74 passing] [storage: SQLite] [MCP]

An MCP server that reads across all your Gmail accounts from one connection.

Most Gmail integrations — including the native connectors — bind a single account per OAuth grant: connect a second inbox and you disconnect the first. gmail-mcp keeps any number of accounts authorized at once. One Google Cloud client authorizes them all, each lands as a row in a local SQLite file, and every tool takes an account argument that routes to the right mailbox. search_all_accounts sweeps all of them in a single query.

Python 3.12+ · MIT · stdio MCP server + auth CLI · local SQLite token store

It's built to be owned completely: runs in-process over stdio, stores tokens in one SQLite file you can inspect, copy, or delete, talks only to Google and your MCP client, and hardcodes no secrets.

It reads, searches, drafts, and labels. It doesn't send — create_draft leaves a draft for you to send yourself. That's a deliberate default (reasoning in Security model), not a hard stance; if you want autonomous send, it's a small addition or a different server.

Contents

• The idea in 30 seconds
• Design notes
• Tools
• Architecture
• Identity & auth model
  • The OAuth model
  • The multi-account model
  • Token lifecycle
  • The headless auth path
• Security model
• Install
• Quickstart
• Configuration
• Register with an MCP client
• Development
• Project layout
• License

The idea in 30 seconds

Authorize N accounts once via the CLI. Then every tool takes an account, and search_all_accounts hits all of them at once:

search_all_accounts(query="invoice newer_than:30d")
  ── [email protected] ───────────────────────────────  from: [email protected]    subject: Invoice #4821    (id 18f...)
  ── [email protected] ─────────────────────────────────  from: [email protected]        subject: March invoice     (id 19a...)

One query, every inbox, each result tagged with its account and carrying the message id — so the agent can chain read_message(account, id) or create_draft(...) next.

Design notes

One OAuth client, many inboxes. A single Google Cloud project and one client_secret.json authorize every account. Adding the tenth inbox is the same one-command flow as the first.

Boring storage. Tokens live in one SQLite file under ~/.gmail-mcp/. No daemon, no keyring dependency, no cloud. Back it up by copying it; revoke an account by deleting a row; inspect it with any SQLite tool.

Least privilege. Four granular scopes — gmail.readonly, gmail.compose, gmail.modify, gmail.settings.basic — never the full-mailbox https://mail.google.com/. It can read, draft, label, and manage filters; it never sends mail, and filters it creates can't forward mail off-account.

Headless-friendly. The auth flow assumes the server may have no browser: it prints a consent URL, binds a fixed port, and you SSH-forward the redirect. Works fine on a desktop too.

Tools

Every tool except list_accounts and search_all_accounts takes an account (the email address). Unknown accounts return an error listing the authorized ones.

Architecture

flowchart TD    subgraph client[Your machine]        Agent[MCP client / agent]        CLI[gmail-mcp-auth CLI]        Server[gmail-mcp stdio server]        Store[("SQLite<br/>~/.gmail-mcp/tokens.db")]        Secret["client_secret.json<br/>one OAuth client"]    end    Google[Google OAuth + Gmail API]
    CLI -->|"loopback OAuth, once per account"| Google    CLI -->|"store refresh token"| Store    Secret -.-> CLI    Agent -->|"tool call (account=...)"| Server    Server -->|"look up + refresh creds"| Store    Secret -.-> Server    Server -->|"read / draft / label"| Google    Server --> Agent

Authorization happens once per account through the CLI (it needs a browser). After that the stdio server reads tokens straight from SQLite, refreshing access tokens on demand and persisting them back. The rest of this section is the "why it works the way it does" detail.

Identity & auth model

How gmail-mcp authenticates to Gmail, juggles multiple accounts under a single OAuth client, refreshes tokens over time, and authorizes accounts on a headless server. If you just want to get running, jump to Quickstart.

The OAuth model

gmail-mcp authenticates using a Google "Desktop app" OAuth client (an installed application in OAuth 2.0 terms), driven by the InstalledAppFlow helper from google-auth-oauthlib.

Why an installed-app / desktop client. Installed apps run on a machine the end user controls, so OAuth treats them as public clients: the client_secret in the downloaded client_secret.json is not assumed to be confidential. That's the right trust model for a local CLI/desktop tool — there's no server-side component that could keep a secret truly secret, and security rests on the user controlling the redirect (the loopback address) rather than on secret confidentiality. It's the client type Google recommends for command-line and desktop tools.

The loopback redirect flow. After you approve consent in a browser, Google redirects the authorization code to http://localhost:<port>/, where a tiny throwaway HTTP server (started by InstalledAppFlow.run_local_server) catches it. gmail-mcp pins this to a fixed port (default 8765, override with GMAIL_MCP_OAUTH_PORT) and runs with open_browser=False so it works on machines with no browser — see The headless auth path.

Scopes requested. Four granular scopes — never the full-mailbox https://mail.google.com/:

gmail.send is not requested. Without it the credential simply has no Gmail API path to send mail — the drafts-only behavior is a property of the grant, not just an omitted tool. gmail.settings.sharing is likewise not requested, so no filter can forward mail to another address. The scope list lives in one place: SCOPES in src/gmail_mcp/config.py.

Adding the filter scope to an existing install: widening SCOPES does not retro-grant already-authorized accounts. Each account must re-run gmail-mcp-auth add to re-consent to the new scope; until it does, the filter tools return a 403 insufficient scope error.

The multi-account model

• One OAuth client authorizes many accounts. You create a single Google Cloud project and one "Desktop app" OAuth client, then run the consent flow once per Gmail account, signing into the account you want to add each time. A single client_secret.json can authorize any number of accounts.
• Each account is a row in SQLite. Every authorized account is stored in the accounts table (~/.gmail-mcp/tokens.db, override with GMAIL_MCP_DB), keyed by email. The row holds the long-lived refresh token, the most recent access-token blob, the granted scopes, and timestamps.
• Tool calls route by the account param. Every tool except list_accounts and search_all_accounts takes an account. The server looks that email up, builds a credential for it, and calls the Gmail API as that account. Unknown accounts return a clear error listing what's authorized. search_all_accounts iterates over every stored row.

flowchart LR    Client[MCP client / agent] -->|"[email protected]"| Server[gmail_mcp.server]    Server --> Store[("accounts table<br/>keyed by email")]    Store -->|"row [email protected]"| CredsA[Credentials a]    Store -->|"row [email protected]"| CredsB[Credentials b]    CredsA --> InboxA["Gmail: [email protected]"]    CredsB --> InboxB["Gmail: [email protected]"]    Secret["client_secret.json<br/>one OAuth client"] -.->|"shared by all rows"| CredsA    Secret -.-> CredsB

Token lifecycle

Initial grant (one-time, per account, via the CLI). The OAuth flow needs a browser, which an MCP tool can't drive cleanly, so authorization lives in the gmail-mcp-auth CLI rather than as a tool.

sequenceDiagram    actor User    participant CLI as gmail-mcp-auth add    participant Browser    participant Google as Google OAuth + Gmail API    participant Store as SQLite token store
    User->>CLI: run `gmail-mcp-auth add`    CLI->>CLI: load client_secret.json,<br/>start loopback server on :8765    CLI-->>User: print consent URL (open_browser=False)    User->>Browser: open URL, sign into target account    Browser->>Google: consent + approve scopes    Google-->>Browser: redirect with authorization code    Browser->>CLI: GET http://localhost:8765/?code=...    CLI->>Google: exchange code for tokens    Google-->>CLI: access token + refresh token    CLI->>Google: users.getProfile (discover email)    Google-->>CLI: emailAddress    CLI->>Store: upsert(email, refresh_token, token, scopes)    CLI-->>User: "Authorized and stored: [email protected]"

• The CLI passes prompt="consent" to force a refresh token to be issued — Google only returns one on a fresh consent. The CLI errors clearly if no refresh token comes back (revoke the app at https://myaccount.google.com/permissions and re-run).
• The account's email is discovered, not typed: after the token exchange the CLI calls users.getProfile and keys the stored row by the returned address.

Per-request refresh (every tool call). Access tokens are short-lived (≈1 hour). On each call the server rebuilds a credential for the target account, lets google-auth refresh it on demand, and persists the refreshed blob back.

sequenceDiagram    participant Client as MCP client / agent    participant Server as gmail_mcp.server    participant Store as SQLite token store    participant Google as Google OAuth + Gmail API
    Client->>Server: tool call ([email protected])    Server->>Store: get(account) → refresh_token + last token    Server->>Server: build Credentials    alt access token still valid        Server->>Google: Gmail API request    else access token expired        Server->>Google: refresh using refresh_token        Google-->>Server: new access token        Server->>Store: update_token(account, new blob)        Server->>Google: Gmail API request    end    Google-->>Server: response    Server->>Store: touch(account) → last_used_at    Server-->>Client: result (email content wrapped as untrusted)

If a refresh fails (revoked grant, expired refresh token), the server raises GmailAuthError with a "re-run gmail-mcp-auth add" message rather than crashing.

Testing vs. Published — the 7-day gotcha. This is the usual "it stopped working after a week" surprise:

• While the OAuth consent screen is in Testing mode, only listed test users can authorize, and refresh tokens issued to an unverified app expire after 7 days — you'd re-run gmail-mcp-auth add weekly.
• Publishing the app (consent screen → Publish app) makes refresh tokens long-lived. Google will warn it's "unverified" — expected and fine for a self-hosted personal tool you don't distribute. For long-lived use, publish. SETUP.md has the exact clicks.

The headless auth path

The typical target is a headless server (no desktop, no browser), but OAuth consent has to happen in a browser. The flow bridges that:

• open_browser=False — the CLI prints the consent URL instead of launching a browser. You open it on your own laptop, signed into the account you're adding.

• Fixed loopback port — after approval Google redirects to http://localhost:<port>/. That "localhost" is the server's loopback, where the CLI listens. The port is fixed (default 8765, GMAIL_MCP_OAUTH_PORT) so you can forward it deterministically.

• SSH port-forward — bridge your laptop's browser to the server's loopback:

  bash

  ssh -L 8765:localhost:8765 you@your-server

  Now when the redirect hits localhost:8765 on your laptop, SSH tunnels it to the server, where the CLI catches the code and finishes the exchange.

Security model

An inbox is full of text other people wrote, so it's a natural place for prompt injection. The standard framing is the lethal trifecta — injection is dangerous when an agent has all three of:

flowchart LR    A[Private data<br/>your mailboxes] --- C{Injection<br/>risk}    B[Untrusted content<br/>any email you receive] --- C    D[Egress channel<br/>a way to send data out] --- C    C -.->|drafts-only removes the obvious one| D    style D stroke-dasharray: 5 5

A mail reader has the first two by nature. A couple of choices keep the third low-stakes:

• Drafts instead of send. create_draft is the outgoing ceiling — there's no send tool and no gmail.send scope. A draft sits in your drafts folder until you send it, so an instruction buried in an email can't make the agent mail your data anywhere. Sensible default, easy to change if you want send.

• Email content is marked as untrusted. Message text the tools return is wrapped in ⟦UNTRUSTED EMAIL CONTENT⟧ delimiters by a single helper (wrap_untrusted in gmail.py), with ids kept outside so tool-chaining still works. The read tools also note in their descriptions that content is data, not instructions. Multi-message responses (search results, threads, cross-account sweeps) emit the fence once around the whole content blob — not once per message — and key each body to a trusted #N id manifest that sits outside the fence. This both cuts delimiter token overhead and keeps real ids exclusively in the trusted region, so an attacker can't smuggle a forged id into a place the agent treats as authoritative.

• Attachments land in one fixed place, and some never land at all. download_attachments writes only under ~/.gmail-mcp/attachments/<message_id>/ (GMAIL_MCP_ATTACHMENT_DIR). There is deliberately no destination argument, because one would be an arbitrary-file-write primitive that an instruction buried in an email could aim at ~/.zshrc. Filenames are attacker-chosen, so they are reduced to inert ASCII basenames (path separators dropped, leading dots stripped, bidi overrides removed, length capped, index-prefixed), and the resolved path is re-checked against the root before the write. Files are written owner-only, with O_NOFOLLOW so a pre-planted symlink can't redirect them.

  Screening happens before any bytes are fetched. It refuses every file type Gmail itself blocks in transit (.exe, .jar, .js, .vbs, .iso, .py, ~50 more), macro-enabled Office documents, executable MIME types, and every attachment on a message Gmail labeled SPAM. All of a filename's dot-suffixes are checked, not just the last, so invoice.pdf.exe is caught. Archives are saved but flagged, since nothing here can look inside one.

  This is a type screen, not a virus scan. Gmail scans attachments server-side but does not expose the verdict through its API. There is no malware field on the message or attachment resource, and attachments.get will serve bytes the Gmail web UI refuses to let you download. A clean verdict here means "not an obvious weapon," never "scanned and safe." The saved file's contents remain untrusted third-party data.

Known limitation. This only governs this server's surface. If the same agent session also has a tool that can reach the open internet (web fetch, HTTP), that's a separate egress path gmail-mcp can't do anything about — pairing it with an arbitrary-egress tool re-opens the trifecta elsewhere. Be deliberate about which tools share a session.

Two more notes: no audit log is implemented (intentionally out of scope), and no secrets are hardcoded — client_id/client_secret come from your downloaded client_secret.json, and tokens live only in your local SQLite store.

Install

Requires Python 3.12+. The PyPI distribution is multi-account-gmail-mcp (the bare gmail-mcp name is taken); it installs the gmail-mcp and gmail-mcp-auth commands.

# From PyPIpip install multi-account-gmail-mcp# or, to get the commands on PATH globally:uv tool install multi-account-gmail-mcp     # or: pipx install multi-account-gmail-mcp# or run without installing:uvx multi-account-gmail-mcp

From source (for development):

git clone https://github.com/cunicopia-dev/gmail-mcp.gitcd gmail-mcppython -m venv .venv && source .venv/bin/activatepip install -e .            # add ".[dev]" for ruff + pytest

This installs two console scripts: gmail-mcp (the stdio server) and gmail-mcp-auth (the account-authorization CLI).

Quickstart

You need a Google "Desktop app" OAuth client (client_secret.json) and one authorization per account. The full click-by-click — creating the Google Cloud project, enabling the Gmail API, publishing the consent screen, and the headless SSH-forward step — is in docs/SETUP.md. The short version:

# 1. Drop your downloaded OAuth client here:mkdir -p ~/.gmail-mcp && mv ~/Downloads/client_secret_*.json ~/.gmail-mcp/client_secret.json
# 2. Authorize an account (prints a URL to open in a browser; repeat per account).#    On a headless server, SSH in with -L 8765:localhost:8765 first.gmail-mcp-auth add
# 3. Confirm what's authorized.gmail-mcp-auth list
# 4. Point your MCP client at the `gmail-mcp` command (see below).

Remove an account later with gmail-mcp-auth remove [email protected].

Configuration

All optional — sane defaults under ~/.gmail-mcp/.

Register with an MCP client

The server speaks stdio. Point your client's mcpServers config at the gmail-mcp command:

{  "mcpServers": {    "gmail": {      "command": "/path/to/gmail-mcp/.venv/bin/gmail-mcp"    }  }}

If gmail-mcp is on PATH, "command": "gmail-mcp" is enough. Override paths explicitly when needed (some clients don't expand ~):

{  "mcpServers": {    "gmail": {      "command": "/path/to/gmail-mcp/.venv/bin/gmail-mcp",      "env": {        "GMAIL_MCP_DB": "/home/you/.gmail-mcp/tokens.db",        "GMAIL_MCP_CLIENT_SECRET": "/home/you/.gmail-mcp/client_secret.json"      }    }  }}

Development

pip install -e ".[dev]"ruff check .pytest                       # 48 tests, no network — the Gmail client is mocked

Tests cover the pure layers — MIME parsing/decoding, label name→id resolution, the untrusted-content wrapper, output formatting, and token-store CRUD against a temp SQLite db.

Project layout

src/gmail_mcp/  server.py    MCP tool definitions + dispatch + per-account routing  gmail.py     Gmail service build, token refresh/persist, MIME parse/format,               wrap_untrusted(), label resolution, MIME message build  store.py     TokenStore — sqlite3 accounts table CRUD  auth.py      gmail-mcp-auth CLI: add / list / remove (loopback OAuth)  config.py    SCOPES + env-overridable pathsdocs/  SETUP.md     step-by-step Google Cloud + account authorizationtests/         store / gmail / server, Gmail client mocked

License

MIT — see LICENSE.