TKasperczyk/thunderbird-mcp

Thunderbird MCP – AI‑friendly bridge for Thunderbird

What it is – A Thunderbird add‑on that runs a tiny local HTTP server and a Node.js bridge so that any Model‑Context‑Protocol (MCP)‑compatible AI assistant (Claude, GPT, local LLMs, etc.) can read, compose, organise and search your mail, contacts, filters and calendar directly from within Thunderbird.

Why it matters – Thunderbird has no official API. Without this bridge an AI cannot see your inbox or help you draft replies. The extension safely exposes ≈40 tools (list accounts, search messages, get full message bodies, send mail, manage filters, contacts, calendar events, …) over MCP, letting AI agents act on your mailbox just like a human would.

How it works

• The add‑on bundles an HTTP server that listens on localhost:8765‑8774 and uses per‑session auth tokens.
• A Node.js script (mcp-bridge.cjs) translates the standard MCP stdio protocol to the local HTTP API, discovers the port/token via a connection file, and handles MCP lifecycle calls (initialize, ping) so the AI can connect even before Thunderbird finishes loading.
• All communication stays on the local machine; no external network traffic is required.

Key capabilities

Area	Tools (selected)	What you can do
Mail	listAccounts, listFolders, searchMessages, getMessage(s), displayMessage, updateMessage, deleteMessages, createFolder …	Browse accounts, search by header/body, read messages in markdown/text/HTML, open them in the UI, mark read/unread, add tags, move/copy, create/delete folders, empty Trash/Junk.
Compose	sendMail, saveDraft, replyToMessage, forwardMessage	Open a review window or (after disabling the Block skipReview safety flag) send directly, save drafts, reply with proper threading, forward with attachments.
Filters	listFilters, createFilter, updateFilter, deleteFilter, reorderFilters, applyFilters	List, create, edit, reorder and manually run mail filters; safety defaults prevent automatic forward/reply actions unless explicitly enabled.
Contacts	searchContacts, getContact, createContact, updateContact, deleteContact	Search, read, create, modify and delete address‑book entries.
Calendar	listCalendars, createEvent, listEvents, updateEvent, deleteEvent	List calendars, create events (review window by default), query events with recurrence expansion, edit or delete them.

Safety & privacy

• Local‑only – The server binds to localhost and uses per‑session tokens; no data leaves your computer.
• Review‑by‑default – Sending mail, creating events with attendees, and automatic filter actions are blocked unless you turn off the Block skipReview preference.
• Encrypted mail – Access to encrypted messages is disabled unless you opt‑in.
• MIME & size limits – Inline images are only included as MCP image blocks (max 1 MiB each, 4 MiB total). HTML bodies larger than 2 MiB are truncated with a clear notice.
• Strict validation – Tag keys, filter strings, contact fields and calendar attendees are validated against Thunderbird’s own rules; malformed inputs cause the whole call to fail rather than being silently corrected.

Typical workflow

1. Install the add‑on in Thunderbird.
2. Start the bridge (node mcp-bridge.cjs) or let a desktop client launch it.
3. An AI model (e.g., Claude) connects via MCP, receives the auth token and port.
4. The model calls tools such as searchMessages to find relevant mail, getMessage to read it, and sendMail (after disabling skipReview) to draft a reply.
5. All actions are performed inside Thunderbird, preserving your existing accounts, signatures and folder structure.

Who might use it – Developers building AI assistants that need deep mailbox access, power users who want their LLM to help triage email, or anyone experimenting with “AI‑as‑a‑personal‑assistant” on a privacy‑preserving, locally‑hosted stack.

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Bottom line – Thunderbird MCP is a genuine, open‑source bridge that gives AI models concrete, well‑documented control over Thunderbird’s mail, contacts, filters and calendar while keeping everything on‑device and guarded by sensible safety defaults.