Thunderbird MCP

Give your AI assistant full access to Thunderbird — search mail, compose messages, manage filters, and organize your inbox. All through the Model Context Protocol.

<p align="center"> <img src="docs/demo.gif" alt="Thunderbird MCP Demo" width="600"> </p>

Inspired by bb1/thunderbird-mcp. Rewritten from scratch with a bundled HTTP server, proper MIME decoding, and UTF-8 handling throughout.

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Why?

Thunderbird has no official API for AI tools. Your AI assistant can't read your email, can't help you draft replies, can't organize your inbox. This extension fixes that -- it exposes 24 tools over MCP so any compatible AI (Claude, GPT, local models) can work with your mail the way you'd expect.

Compose tools open a review window before sending. Nothing gets sent without your approval.

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How it works

                    stdio              HTTP (localhost:8765)
  MCP Client  <----------->  Bridge  <--------------------->  Thunderbird
  (Claude, etc.)           mcp-bridge.cjs                    Extension + HTTP Server

The Thunderbird extension embeds a local HTTP server. The Node.js bridge translates between MCP's stdio protocol and HTTP. Your AI talks stdio, Thunderbird talks HTTP, the bridge connects them. The bridge handles MCP lifecycle methods (initialize, ping) locally, so clients can connect even before Thunderbird is fully loaded.

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What you can do

Mail

Tool	Description
listAccounts	List all email accounts and their identities
listFolders	Browse folder tree with message counts — filter by account or subtree
searchMessages	Find emails by subject, sender, recipient, date range, read status, or within a specific folder
getMessage	Read full email content with optional attachment saving -- includes inline CID images
getRecentMessages	Get recent messages with date and unread filtering
updateMessage	Mark read/unread, flag/unflag, move between folders, or trash -- supports bulk via messageIds
deleteMessages	Delete messages — drafts are safely moved to Trash
createFolder	Create new subfolders to organize your mail

Compose

Tool	Description
sendMail	Open a compose window with pre-filled recipients, subject, and body
replyToMessage	Reply with quoted original and proper threading
forwardMessage	Forward with all original attachments preserved

All compose tools open a window for you to review and edit before sending.

Filters

Tool	Description
listFilters	List all filter rules with human-readable conditions and actions
createFilter	Create filters with structured conditions (from, subject, date...) and actions (move, tag, flag...)
updateFilter	Modify a filter's name, enabled state, conditions, or actions
deleteFilter	Remove a filter by index
reorderFilters	Change filter execution priority
applyFilters	Run filters on a folder on demand — let your AI organize your inbox

Full control over Thunderbird's message filters. Changes persist immediately. Your AI can create sorting rules, adjust priorities, and run them on existing mail.

Contacts & Calendar

Tool	Description
searchContacts	Look up contacts from your address books
listCalendars	List all calendars with read-only, event, and task support flags
createEvent	Create a calendar event -- opens a review dialog, or set skipReview to add directly
listEvents	Query events by date range with recurring event expansion
updateEvent	Modify an event's title, dates, location, or description
deleteEvent	Delete a calendar event by ID
createTask	Open a pre-filled task dialog for review

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Setup

1. Install the extension

git clone https://github.com/TKasperczyk/thunderbird-mcp.git

Install dist/thunderbird-mcp.xpi in Thunderbird (Tools > Add-ons > Install from File), then restart. A pre-built XPI is included in the repo — no build step needed.

2. Configure your MCP client

Add to your MCP client config (e.g. ~/.claude.json for Claude Code):

{
  "mcpServers": {
    "thunderbird-mail": {
      "command": "node",
      "args": ["/absolute/path/to/thunderbird-mcp/mcp-bridge.cjs"]
    }
  }
}

That's it. Your AI can now access Thunderbird.

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Security

The extension listens on localhost:8765 only. No remote access. However, any local process can reach it while Thunderbird is running — keep this in mind on shared machines.

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Troubleshooting

Problem	Fix
Extension not loading	Check Tools > Add-ons and Themes. Errors: Tools > Developer Tools > Error Console
Connection refused	Make sure Thunderbird is running and the extension is enabled
Missing recent emails	IMAP folders can be stale. Click the folder in Thunderbird to sync, or right-click > Properties > Repair Folder
Tool not found after update	Reconnect MCP (/mcp in Claude Code) to pick up new tools

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Development

# Build the extension
./scripts/build.sh

# Test the HTTP API directly
curl -X POST http://localhost:8765 \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

# Test the bridge
echo '{"jsonrpc":"2.0","id":1,"method":"tools/list"}' | node mcp-bridge.cjs

After changing extension code: remove from Thunderbird, restart, reinstall the XPI, restart again. Thunderbird caches aggressively.

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Project structure

thunderbird-mcp/
├── mcp-bridge.cjs              # stdio <-> HTTP bridge
├── extension/
│   ├── manifest.json
│   ├── background.js           # Extension entry point
│   ├── httpd.sys.mjs           # Embedded HTTP server (Mozilla)
│   └── mcp_server/
│       ├── api.js              # All 24 MCP tools
│       └── schema.json
└── scripts/
    ├── build.sh
    └── install.sh

Known issues

• IMAP folder databases can be stale until you click on them in Thunderbird
• Email bodies with control characters are sanitized to avoid breaking JSON
• HTML-only emails are converted to plain text (original formatting is lost)
• Recurring calendar event CRUD operates on the series, not individual occurrences

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License

MIT. The bundled httpd.sys.mjs is from Mozilla and licensed under MPL-2.0.