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.

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 36 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 by default. Set skipReview to send directly when you've already approved the content upstream. Nothing gets sent without your approval.

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How it works

                    stdio              HTTP (localhost:8765-8774)
  MCP Client  <----------->  Bridge  <--------------------->  Thunderbird
  (Claude, etc.)           mcp-bridge.cjs                    Extension + HTTP Server

The Thunderbird extension embeds a local HTTP server with session-scoped auth tokens. The Node.js bridge translates between MCP's stdio protocol and HTTP, discovering the port and token automatically via a connection file. 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	Search by subject, sender, recipient, body preview, date range, or tags. Multi-word queries are AND-of-tokens (every word must appear somewhere). Prefix with from:, subject:, to:, or cc: to restrict to one field. Set searchBody: true for full-text body search via Thunderbird's Gloda index. Supports includeSubfolders, countOnly, and offset-based pagination. Results include threadId and preview snippet. By default, dedupByMessageId collapses the same RFC Message-ID found in multiple folders/labels into one row and reports the other folder paths in dupLocations; set dedupByMessageId: false to return every location.
getMessage	Read full email content -- bodyFormat: markdown (default), text, or html. Set rawSource: true for the complete RFC 2822 source (all headers + MIME parts). Optional attachment saving. Includes inline CID images.
getMessages	Read full email content for up to the configured batch limit in one call (default 10, max 20). Uses the same bodyFormat, rawSource, and attachment options as getMessage; each item supplies messageId and folderPath.
getRecentMessages	Get recent messages with date, unread, and tag filtering. Supports pagination. Results include threadId and preview.
displayMessage	Open a message in Thunderbird's GUI -- 3pane (default), tab, or window mode
updateMessage	Mark read/unread, flag/unflag, add/remove tags, 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
renameFolder	Rename an existing mail folder
deleteFolder	Delete a folder (moves to Trash, or permanently deletes if already in Trash)
moveFolder	Move a folder to a new parent within the same account
emptyTrash	Permanently delete all messages in Trash (including subfolders)
emptyJunk	Permanently delete all messages in Junk/Spam (including subfolders)

Compose

Tool	Description
sendMail	Compose a new email -- opens a review window, or set skipReview to send directly
replyToMessage	Reply with quoted original and proper threading -- supports skipReview
forwardMessage	Forward with all original attachments preserved -- supports skipReview

All compose tools open a window for you to review and edit before sending by default. Set skipReview: true to send directly when you've already approved the content. Attachments can be file paths or inline base64 objects.

Compose tools validate the from identity strictly -- if the specified sender doesn't match any configured Thunderbird identity, the tool returns an error instead of silently substituting another account.

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

Tool	Description
searchContacts	Search contacts across all address books by email or name. Supports maxResults.
createContact	Create a new contact in any writable address book
updateContact	Update an existing contact's email, name, or display name
deleteContact	Delete a contact by UID

Calendar

Tool	Description
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. Accepts status: tentative | confirmed | cancelled (VEVENT STATUS per iCal RFC 5545).
listEvents	Query events by date range with recurring event expansion. Returns status on each event.
updateEvent	Modify an event's title, dates, location, description, or status
deleteEvent	Delete a calendar event by ID
createTask	Open a pre-filled task dialog for review
listTasks	List tasks/to-dos from calendars -- filter by completion status, due date, or calendar
updateTask	Update a task's title, due date, description, priority, completion status, or percent complete

Access Control

Tool	Description
getAccountAccess	View which accounts the MCP server can access

Account and tool access are configured via the extension settings page (Tools > Add-ons > Thunderbird MCP > Options). Access control is not MCP-exposed -- only the user can change it.

The same settings page has a "Send Safety" section: toggle Block skipReview to reject sendMail / replyToMessage / forwardMessage calls that pass skipReview: true. The review-window path still works, so clients stay usable -- they just can't send silently.

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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"]
    }
  }
}

Sandbox-aware connection discovery

The bridge re-discovers connection.json on every cache miss. It tries these locations in order:

1. THUNDERBIRD_MCP_CONNECTION_FILE, if set
2. Native temp dir: <os.tmpdir()>/thunderbird-mcp/connection.json
3. macOS fallback: /var/folders/*/*/T/thunderbird-mcp/connection.json owned by the current user
4. Linux Snap: Thunderbird's live TMPDIR from /proc/<pid>/environ, plus the official snap fallback under ~/Downloads/thunderbird.tmp
5. Linux Flatpak / Betterbird Flatpak: $XDG_RUNTIME_DIR/app/*/thunderbird-mcp/connection.json

This covers native installs, the official Thunderbird snap, Thunderbird Flatpak, Thunderbird Beta Flatpak, and Betterbird Flatpak without changing the extension side. If multiple sandbox candidates exist at once, the bridge tries the newest file first. Set THUNDERBIRD_MCP_CONNECTION_FILE to force a single explicit path.

Example override:

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

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

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Security

• Auth tokens: The HTTP server requires a session-scoped bearer token. Generated on startup, written to <TmpD>/thunderbird-mcp/connection.json with 0600 permissions. The bridge re-discovers that file automatically across native installs, Snap, Flatpak, Betterbird Flatpak, and macOS temp directories.
• Dynamic port: Tries ports 8765-8774, records the actual port in the connection file. No hardcoded port dependency.
• Account access control: Restrict which email accounts are visible to MCP clients via the settings page. Changes take effect immediately.
• Tool access control: Disable specific tools via the settings page. Disabled tools are hidden from tools/list and blocked at dispatch.
• Localhost only: By default, the server binds to localhost only. The "Listen on all interfaces" option in settings binds to all IPv4 interfaces for WSL, Docker, or remote access. This exposes the MCP server to every device on your local network. Only enable on trusted networks. Auth token is always required.

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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
Bridge can't find connection.json	Set THUNDERBIRD_MCP_CONNECTION_FILE explicitly if your environment uses a non-standard temp/runtime path
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
searchBody returns no results	IMAP accounts need offline sync enabled for Gloda to index message bodies
rawSource fails on IMAP	Requires local/offline message copy. Enable offline sync or click the message first to cache it.

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Development

# Build the extension
./scripts/build.sh

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

# Test the HTTP API directly.
# On Snap / Flatpak / Betterbird Flatpak / macOS, point CONN_FILE at the
# real file or export THUNDERBIRD_MCP_CONNECTION_FILE first.
CONN_FILE="${THUNDERBIRD_MCP_CONNECTION_FILE:-/tmp/thunderbird-mcp/connection.json}"
TOKEN=$(jq -r .token "$CONN_FILE")
PORT=$(jq -r .port "$CONN_FILE")
curl -X POST http://127.0.0.1:$PORT \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $TOKEN" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

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 (auth, port discovery)
├── extension/
│   ├── manifest.json
│   ├── background.js           # Extension entry point
│   ├── httpd.sys.mjs           # Embedded HTTP server (Mozilla)
│   ├── options.html            # Settings page UI
│   ├── options.js              # Settings page logic
│   ├── icons/                  # Extension icons
│   └── mcp_server/
│       ├── api.js              # All 36 MCP tools + auth + access control
│       └── schema.json
├── test/                       # Test suite (node:test, zero dependencies)
└── scripts/
    ├── build.sh
    └── install.sh

Known issues

• IMAP folder databases can be stale until you click on them in Thunderbird
• HTML-only emails are converted to plain text (original formatting is lost)
• Recurring calendar event CRUD operates on the series, not individual occurrences
• IMAP folder operations (rename, delete, move) are async -- verify with listFolders after
• Combining tags with move/trash on IMAP may not preserve tags on the moved copy -- use separate calls
• Pre-existing Thunderbird filters with cross-account move/copy targets are not restricted by account access control
• searchBody on IMAP without offline sync only searches headers (Gloda limitation)
• rawSource requires offline message copy for IMAP -- online-only messages will error

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License

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