mail-mcp

An Apple Mail MCP server with a supply chain small enough to read in an afternoon: zero runtime dependencies, no network code, no shell, and no way to send mail. It drives Mail.app through its scripting interface (JXA over osascript) and exposes thirteen tools for reading mail, listing structure, handling attachments, and creating drafts.

Everything load-bearing here traces to measurements on real hardware, recorded in docs/apple-mail/ and re-checkable with node research/verify.mjs.

The security posture, stated plainly

This server cannot send mail, and that is the design, not a gap.

• There is no send tool, no send code path, and no code that could grow one quietly: a test walks the dependency closure and fails if anything imports node:net, node:tls, node:http, node:https, node:dgram, calls fetch, or contains a send( call in a Mail script. Do not add a send tool; a draft-then-send flow with an in-band confirmation token does not actually establish human review, because a model can chain both calls in one turn. The user reviews drafts in Mail.app and presses Send there.

• Drafts are the only mutation. No delete, no move, no mark-as-read, no rule editing. Email content is attacker-controlled input to any model reading it; the small write surface bounds what injected instructions can do.

• No credentials, no sockets, no Keychain. Mail.app does its own syncing; this server never sees a password or opens a connection.

• save-attachment is the only filesystem writer. It writes only under an allowlisted root (MAIL_MCP_SAVE_ROOT, default ~/Downloads), resolves symlinks before checking containment, sanitizes filenames from mail, and never overwrites. There is deliberately no tool that returns attachment bytes into the conversation.

• No user value is ever interpolated into script text. Scripts are static files on disk; values travel as argv, spawned without a shell.

• package.json has no dependencies key. Ever. A test enforces this too.

Related MCP server: mail-mcp

Requirements

• macOS with Mail.app configured (built against Mail 16.0 on macOS 26.x)

• Node.js 20 or newer

• Automation permission for whatever runs the server (see below)

Install and register

No build step and no dependencies to install:

git clone https://github.com/007hacky007/mail-mcp.git
cd mail-mcp

Register with Claude Code (available in every session):

claude mcp add --scope user mail-mcp -- node "$(pwd)/src/index.mjs"

Or for the current project only:

claude mcp add mail-mcp -- node "$(pwd)/src/index.mjs"

For any other MCP host, configure a stdio server running node /absolute/path/to/mail-mcp/src/index.mjs.

Verify with the host's tooling (claude mcp list should show mail-mcp ... Connected), then call the doctor tool.

Automation permission

On the first call into Mail, macOS prompts to allow the host application to control Mail.app. Approve it. To check or repair the grant: System Settings > Privacy & Security > Automation, find the host app (Terminal, Claude, etc.), enable Mail. The doctor tool reports whether the grant is working.

The ad-hoc-signed Node problem

TCC identifies programs by code signature. A Homebrew-installed Node is ad-hoc signed and its signature changes on every upgrade, so macOS forgets the Automation grant and prompts again after each brew upgrade. If the re-prompting bothers you, use the official Node.js installer (Developer ID signed, stable identity) at a stable path. doctor reports which kind of Node is running.

Tools

Things worth knowing before filing a bug

• Message ids are per-mailbox integers and do not survive moves. Every tool returns the full mailbox path with the id, and lookups need both. If a message was moved since you listed it, re-list or search again.

• Size guards are deliberate. Bulk reads degrade worse than linearly with mailbox size (measured: a 52k-message mailbox is far more than 3x slower than a 17k one). Mailboxes over the guard are refused or skipped and reported, never silently dropped. Raise maxMessages per call to scan them anyway and expect tens of seconds.

• Search covers subject and sender, not bodies. Fetching every body through the scripting bridge would take minutes and gigabytes.

• A failed operation never looks like an empty result. Transport failures (Mail unresponsive, timeout) surface as errors; domain refusals name the real candidates; partial scans label their totals as floors and list what was skipped.

• Ambiguity is refused, not guessed. Real mailboxes can have two same-named siblings (this machine has twin Junk mailboxes in one account); a path matching more than one mailbox is an error naming them.

• Gmail accounts may hide standard mailboxes from the scripting bridge. On this machine the Gmail-backed account exposes no All Mail, no [Gmail] container, and no Drafts mailbox; its INBOX is real and holds the mail. Created drafts for such an account exist in Mail's unified Drafts even when no per-account Drafts path can list them.

Configuration

Testing

npm test                  # tier 1: 219 unit tests, no Mail.app, runs anywhere
node research/verify.mjs  # tier 2: replays every recorded probe against real Mail

Tier 1 gates every commit: input guards, MIME parsing, path containment, error mapping, and the no-network/no-send/no-deps enforcement tests. Tier 2 is the drift detector: it fails when a macOS update changes Mail's object model or performance characteristics that this design rests on (bulk fetch, byId cost, mailbox structure).

Tier 3 is drafts: creating them is the only mutation, so automated runs are manual-by-choice. The live checklist used during development is described in docs/apple-mail/README.md (draft recipes section); it creates clearly labeled test drafts that you delete afterwards.

Architecture

src/mcp/     stdio JSON-RPC framing: initialize, tools/list, tools/call
src/tools/   one file per tool: validate input, call, shape output
src/mail/    domain logic that runs in Node: MIME parsing, path containment
src/jxa/     the runner plus one .js script per operation, run via osascript

Scripts are ordinary files, independently runnable from a terminal for debugging (osascript -l JavaScript src/jxa/list-accounts.js). The runner serializes all Mail calls (Mail's scripting dispatch is single-threaded), charges queue wait against each call's own deadline, kills overruns with SIGKILL, and treats non-JSON output as a transport failure, never as data.

The knowledge behind every design decision lives in docs/apple-mail/: measured costs, the whose-clause trap, message identity semantics, the draft-content trap, and the corrections to folklore that turned out to be wrong on real hardware.

License

No license granted yet. All rights reserved.