MCP server de Multi-Account Gmail

gmail-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.

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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

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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")

  ── personal@gmail.com ───────────────────────────────
  from: billing@acme.com    subject: Invoice #4821    (id 18f...)

  ── work@company.com ─────────────────────────────────
  from: ap@vendor.io        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.

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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.

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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.

Tool	Arguments	Returns
list_accounts	—	Authorized accounts + last-used time. Discover valid account values.
search_messages	account, query, max_results=20	Message summaries (Gmail search syntax) with ids.
read_message	account, message_id, format="full", max_body_chars?	Decoded headers, plaintext body (HTML stripped if needed), attachment metadata. Body capped by default; pass max_body_chars=0 for the full body.
read_thread	account, thread_id, max_body_chars?	Every message in the thread, in order. Each body capped by default; max_body_chars=0 for full.
download_attachments	account, message_id, index?	Save a message's attachments to disk and return absolute paths. Address them by the #N shown in read_message; omit index for all of them. Fixed download root, no destination argument. Dangerous file types and anything on a spam-labeled message are refused.
search_all_accounts	query, max_results_per_account=10	One search across every account, each result tagged by account.
create_draft	account, body, to?, subject?, cc?, bcc?, html=false, reply_to_message_id?, reply_all=false, from_addr?	A draft (not sent). Returns the draft id. With reply_to_message_id the draft is a reply inside that message's thread: recipient, subject, In-Reply-To, References and the thread id come from it, and to/subject become optional overrides. Without it, to and subject are required. from_addr sets the From header for a verified send-as alias; it defaults to the account address.
list_drafts	account, max_results=20	Draft ids in the account.
list_labels	account	The account's labels (name + id).
create_label	account, name	Create a user label (nest with /). Idempotent: an existing name (case-insensitive) returns its id and creates nothing.
modify_labels	account, selection (message_id | message_ids | query), add?, remove?	Add/remove labels on a selection (one id, a list, or everything a query matches), batched 1000/call. General mutator: archive = remove INBOX, mark-read = remove UNREAD, star = add STARRED.
trash	account, selection (message_id | message_ids | query)	Move a selection to Trash (recoverable 30 days; not permanent delete). Refuses an empty selection.
bulk_action	account, action, selection (message_id | message_ids | query)	Friendly verb layer over modify_labels. action ∈ archive/unarchive/mark_read/mark_unread/star/unstar/spam/unspam/trash/untrash. Batched 1000/call; refuses an empty selection.
read_messages	account, message_ids | query, max_results=25	Batch-read full content of many messages in one call (vs. N read_message calls).
count_messages	query, account?, all_accounts=false	Count matches without fetching content — blast-radius check before a bulk action. all_accounts gives a per-account breakdown + total.
list_filters	account	The account's filters: id, criteria, actions (label ids shown as names).
create_filter	account, one of from_address/to_address/subject/query/has_attachment, plus an action (archive/mark_read/delete/star or add_labels/remove_labels)	A server-side rule applied to incoming mail. Can't forward off-account.
delete_filter	account, filter_id	Remove a filter by id (leaves already-acted-on mail alone).

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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.

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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/:

Scope	What it grants
gmail.readonly	Read mail and metadata: search messages/threads, read bodies, list labels and drafts. Read-only — cannot modify anything.
gmail.compose	Create, update, and manage drafts. Used only by create_draft.
gmail.modify	Add/remove labels on messages and create labels. Used by modify_labels, bulk_action, trash and create_label.
gmail.settings.basic	List, create, and delete filters. Used by list_filters/create_filter/delete_filter. Does not grant forwarding-address changes (that's gmail.settings.sharing, not requested).

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] -->|"account=a@x.com"| Server[gmail_mcp.server]
    Server --> Store[("accounts table<br/>keyed by email")]
    Store -->|"row a@x.com"| CredsA[Credentials a]
    Store -->|"row b@y.com"| CredsB[Credentials b]
    CredsA --> InboxA["Gmail: a@x.com"]
    CredsB --> InboxB["Gmail: b@y.com"]
    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: you@gmail.com"

• 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 (account=you@gmail.com)
    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:

  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.

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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.

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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 PyPI
pip 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.git
cd gmail-mcp
python -m venv .venv && source .venv/bin/activate
pip 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).

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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 you@gmail.com.

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Configuration

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

Variable	Default	Purpose
GMAIL_MCP_DB	~/.gmail-mcp/tokens.db	SQLite token store path.
GMAIL_MCP_CLIENT_SECRET	~/.gmail-mcp/client_secret.json	Downloaded Google OAuth client.
GMAIL_MCP_OAUTH_PORT	8765	Fixed loopback port for the auth flow (forward this over SSH on a headless box).
GMAIL_MCP_ATTACHMENT_DIR	~/.gmail-mcp/attachments	Download root for download_attachments. Files land in a per-message subdirectory. This is the only location the server writes to.
GMAIL_MCP_MAX_ATTACHMENT_BYTES	26214400 (25 MB)	Per-attachment size ceiling. Gmail's own limit is 25 MB, so this refuses nothing Gmail would deliver. 0 (or negative) means unlimited.
GMAIL_MCP_MAX_BODY_CHARS	500	Default per-message body cap for read_message/read_thread. Deliberately tight so reads are cheap by default; 0 (or negative) means unlimited, and a per-call max_body_chars argument overrides it.

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