Mail Index MCP Server

mail-index

mail-index downloads a preview of your whole inbox to your machine, then smartly fetches the full text of the messages that matter as you use it. That local index lets your AI agent run true summarization and recall over your entire mailbox — instead of being trapped behind Gmail's search bar.

It works through a local MCP server, so any agent (Claude, Codex, any MCP client) can query it. Local-first — the index never leaves your machine. Read-only — it never sends or mutates your mail.

Status: v1.0 — published. Progressive sync, the correspondence graph, the interest engine, curation, the full 18-tool MCP surface, and the write-back loops are built and tested — and mail-index is live on npm with a .mcpb bundle. Still in progress: the bundled Option A OAuth client and signed one-click installers. Architecture lives in docs/PLAN.md; start with docs/INSTALL.md.

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How it works

1. Progressive sync — metadata for the whole mailbox in minutes; bodies fetched selectively.
2. Graph — contacts, domains, threads; centrality + communities over your human (non-bulk) mail.
3. Interest — an engagement score per contact from read/reply/star/importance signals. A seed for your curation, not an autonomous decision.
4. Curate — you (via your agent, or a CLI wizard) confirm who/what matters; that profile drives which bodies get fetched.
5. Query — your agent searches, traverses the graph, and reads the messages that matter, all locally via MCP.

Quick start

Requires Node 24+ and a Gmail MailSource adapter — gog (recommended) or gws. Reading Gmail needs a Google OAuth client, and you get one two ways: use the mail-index beta client (skip Google Cloud entirely; request access to join the ~100-user test list) or bring your own Google Cloud client (no cap, no request — we walk you through it). See docs/INSTALL.md §2 and docs/oauth-and-verification.md.

npm install -g mail-index                    # or: pnpm add -g mail-index

mail-index init                              # scaffold the config
# …connect a mailbox (own OAuth client, read-only) — see docs/INSTALL.md §2 / agent-install.md…
mail-index sync  --account personal --since 6mo
mail-index graph build --account personal
mail-index search "that contract we discussed"

(Prefer source? git clone …, pnpm install && pnpm build, then run the bins as node dist/cli/index.js ….)

Add to Claude

The MCP server registers in one step, but it still needs a mailbox connected first (see the walkthrough). A .mcpb/claude mcp add only adds the server — it doesn't install the adapter, sign you in, or sync.

• Claude Code: claude mcp add --transport stdio mail-index -- npx -y -p mail-index mail-index-mcp
• Any MCP client (manual):

  { "mcpServers": { "mail-index": { "command": "mail-index-mcp" } } }
  

• Claude Desktop: download the .mcpb bundle and double-click it (unsigned during beta — you may need to allow it in System Settings). A signed all-in-one installer that also installs the adapter, signs you in, and syncs is still in progress; there is no claude:// install link.

Teach your agent the common moves. The MCP server already tells the agent when to reach for it (purchases, receipts, bookings, "who said what", "catch me up"), and the repo ships a Claude Agent Skill with the typical recipes (find purchases, catch up, find a contact's mail, summarize a sender). Drop it in for Claude Code/Desktop:

mkdir -p ~/.claude/skills && cp -R skills/mail-index ~/.claude/skills/

Full walkthrough (auth, curation, enrichment, scheduled sync, desktop-app gotchas) → docs/INSTALL.md. Driving setup with an agent → docs/agent-install.md.

What to expect — time & storage

The index keeps metadata for every message and full text only where it earns it, so it grows with message count, not mailbox size — about 1.5% of your Gmail. First sync runs ~50 messages/min (one-time, incremental after); search is instant. Start with --since 1mo for value in minutes, then expand. Sizing table & growth path → docs/INSTALL.md §9.

Why it's lighter than Gmail search

Stock Gmail-API MCPs are query-based lookup tools — exact query, a network round-trip per call, raw payloads dumped into the model's context. mail-index answers vague questions from a local recall index. Across a 100-question suite on a real mailbox it answered every question for 15× fewer tokens — and the gap widens exactly where a query-based MCP has no primitive at all: summarizing, relationships, and commitments.

Per-category tables, the read-one-message comparison, the tool-by-tool landscape, and how to reproduce it all → docs/COMPARISON.md.

Stack

TypeScript · node:sqlite (no native deps) · SQLite FTS5 · Graphology · @modelcontextprotocol/sdk. Node 24+. Pluggable MailSource adapters; ships two Gmail transports — gog (recommended) and Google's gws.

CLI

Two bins ship: mail-index (CLI) and mail-index-mcp (the stdio MCP server).

mail-index init                          Scaffold the operator config + data dir
mail-index sync    --account <a> [--since 30d|1mo] [--all] [--query <q>] [--limit N]
mail-index sync    --all-accounts        Sync every account by its policy presets
mail-index enrich  --account <a> [--profile | --rule direct|all] [--sender <s>] [--match <fts>] [--limit N]
mail-index graph   build [--account <a> | --all-accounts]
mail-index curate  [--account <a>]       Interactive curation wizard (no-agent fallback)
mail-index compact [--account <a>] [--now]   Demote summarized bulk bodies (ADR-0003)
mail-index search  <terms> [--account <a>] [--limit N] [--enrich]
mail-index show    <account:message-id>  Print a message (auto-enriches a meta row)
mail-index open    <account:message-id>  Print the provider web URL (no fetch)
mail-index status  [--json]              Per-account freshness + counts

Documentation

• docs/INSTALL.md — generic onboarding (install, authenticate a MailSource, init, sync, curate, enrich, add the MCP server, scheduled-sync snippet).
• docs/MCP.md — the 18-tool MCP reference for agent integrators: args, compact result shapes, the index_as_of freshness + command-handback contracts.
• docs/ADAPTERS.md — the MailSource contract and how to write + contract-test a new adapter.
• docs/PLAN.md — architecture, data model, and the key decisions (ADR digest).
• SECURITY.md + docs/THREAT-MODEL.md — privacy posture, trust boundaries, prompt-injection stance, and a "verify our claims yourself" runbook. The local-only promise is enforced in CI by an egress guard test.

About

Built by Unsold Group — a travel & insurtech company building the groundwork to operate as an AI-native business: local-first, agent-native infrastructure that gives AI real, queryable context to work from. mail-index is one piece of that — giving agents durable memory of a mailbox without handing them the keys to it.

More: unsold.group/al

Feedback & contact

There's no telemetry — we only know what you tell us, so feedback is genuinely welcome:

• 💬 Discussions — questions, ideas, how you use it
• 🐞 Report a bug · 💡 Request a feature
• 🔒 Security/privacy issues → SECURITY.md (private)
• 🌐 unsold.group/al

Inside your agent you can also just say "report a mail-index bug" — the MCP server points the agent to a GitHub link for you to submit (it never sends anything itself). See SUPPORT.md.

License

MIT