MCP for Thunderbird

About this Add-on

MCP for Thunderbird lets AI apps on your computer work with the mail in the Thunderbird mail app, within limits you set. AI apps such as Claude Desktop, Claude Code, Codex and Cursor connect to outside tools through the Model Context Protocol (MCP), an open standard. This add-on gives them a set of mail tools: search your mail, read a message, tidy your inbox, write a draft for you to check. You choose which accounts they may use and what they may do, and you can pause them at any time from the toolbar button.

HOW IT WORKS

There are two parts. The add-on runs in the mail app and does the mail work through the standard add-on interfaces. The host program is a small separate program on the same computer, started through native messaging when the mail app starts and stopped when it closes. AI apps talk to the host program, and the host program passes their requests to the add-on. The host program is a separate download: install it for your system from https://github.com/wadejbeckett/mcp-for-thunderbird/releases and run its setup once. Without it the toolbar button shows "not connected" and nothing else happens.

WHAT AI APPS CAN DO

The tools come in groups that you switch on or off in the options:

- Read: list accounts and folders, search mail, read one message, list a conversation, save an attachment to a folder you choose, and describe a message filter for you to create.
- Organise: mark as read or flagged, add or remove tags, move or copy to another folder, archive, and move to Trash.
- Draft: save a message, reply or forward to Drafts, or open a filled-in compose window for you to check and send.
- Contacts: look people up in your address books.
- Sending: send a message with no window, only to recipients you have listed. Off unless you turn it on.

No tool deletes mail for good, empties Trash or Junk, deletes a folder or changes account settings.

GETTING STARTED

1. Install the host program from the releases page and run its setup; the page explains each system.
2. Install this add-on. Its setup page opens: tick the accounts AI apps may use, choose what they may do, and tick the AI apps to set up.
3. Restart your AI app and ask it, for example, "What needs my attention in my inbox today?"

The options page (Add-ons and Themes, then this add-on's Options) holds every setting, the connection details for an AI app you set up by hand, and an activity log of the last 500 requests.

SAFETY DEFAULTS

- No accounts until you tick them, and no sending: with the default settings nothing an AI app does can send mail or delete anything for good.
- Search returns pointers only (sender, subject, date, folder, flags), never message text. An AI app reads the text of a message only by asking for that one message.
- Message text is marked as untrusted content, with hidden text, scripts and invisible characters removed as far as practical, so a message cannot easily pass itself off as instructions to the AI app.
- Local only, with an access key: the host program listens only on your own computer and answers only requests that carry its key.
- Pause from the toolbar at any time; the activity log shows what each app did.

PRIVACY

The add-on sends the host program mail data only as the results of tool calls an AI app made, within your settings: the names and addresses of the accounts you enabled, their folders and tags, message headers, the text of the messages the AI app asks to read, the bytes of the attachments it asks to save, and contacts when the contacts group is on. The host program passes those results only to AI apps on the same computer that hold its access key. The AI app sends what it reads to its own vendor, under that vendor's terms. Nothing goes to the author of this add-on: it has no server, no account and no telemetry. The full privacy policy is below and in the repository.

REQUIREMENTS

Thunderbird 140 ESR or later on Linux; the host program; and an AI app that supports MCP. Windows and macOS are not supported yet: their packages are built and tested in CI, but have not been checked by hand on a real PC or Mac. On 140 ESR the two tools that save a draft or send without a window are not offered; they are offered from version 153 on, and the compose window works on every supported version.

MCP for Thunderbird is free software under the GNU General Public License, version 3 or later, with its source at https://github.com/wadejbeckett/mcp-for-thunderbird. It is not made by, endorsed by or affiliated with Mozilla or MZLA Technologies.

Version Information

PRIVACY POLICY

Last updated: 3 November 2026.

This policy covers MCP for Thunderbird: the Thunderbird add-on and the host program it works with. MCP for Thunderbird lets AI apps on your computer, such as Claude Desktop, Claude Code, Codex or Cursor, work with the mail in Thunderbird, within limits you set in Thunderbird. MCP for Thunderbird is published by Wade J. Beckett, whose company is Noiz.

In short

MCP for Thunderbird moves mail data only between Thunderbird and AI apps on your own computer, and only what an AI app asks for within your settings. It has no server of its own and collects nothing about you. The AI app you connect sends what it reads to its vendor, as it does with anything else you give it.

What data goes where

MCP for Thunderbird has two parts. The add-on runs in Thunderbird. The host is a separate program on the same computer, started by Thunderbird through its native messaging channel; this policy calls it "the native program". AI apps talk to the native program, and the native program passes their requests to the add-on.

- MCP for Thunderbird sends the native program mail data only as tool results: the names and addresses of the accounts you enabled, their folders and tags, message headers, the text of messages the assistant asks to read, the bytes of attachments it asks to save, and contacts when the contacts group is turned on.
- The native program passes those results only to AI apps on the same computer that hold its access key.
- The AI app sends what it reads to its vendor, under that vendor's own terms and privacy policy.
- Nothing goes to Noiz or to the authors of MCP for Thunderbird.
- There is no telemetry: MCP for Thunderbird collects no usage data, crash reports or analytics.

Some more detail on each point:

- Only what is asked for, within your settings. A tool result exists only because an AI app asked for it, and only for the accounts you ticked, outside the folders you excluded, and in the tool groups you turned on. There are two exceptions. Contacts are not limited by accounts or folders: see Contacts below. And Thunderbird keeps tags for the whole profile, not per account, so mail_tags returns every tag's name and colour once at least one account is ticked, including tags you use only in accounts you did not tick. Message headers here means sender, recipients, Reply-To, subject, date, folder, flags and tags, the names, sizes and types of attachments and the link of an attachment the message only links to, and the sender authentication results (SPF, DKIM and DMARC) your mail server recorded. When an AI app asks for them, it also gets every other header of the one message it reads, such as Received and List-Unsubscribe, but never Bcc, Resent-Bcc or any other header that lists blind-copy recipients. Search results never include message text. The text of a message is sent only when an AI app asks to read that one message.
- Attachments. When an AI app saves an attachment, its bytes go to the native program, which writes them into the attachment folder you chose in the options. A plain-text attachment can instead be returned as text. Attachments over 50 MiB are refused.
- Contacts. Address book entries (names, email addresses and organisation, with the names of the address books they are in) and, when an AI app asks for them, mailing lists (their names, nicknames and members) are sent only when you have turned on the contacts group. Address books belong to the whole Thunderbird profile, not to one account, so the contacts group returns entries from every local address book whatever accounts you ticked or folders you excluded. That includes Collected Addresses, where Thunderbird keeps the addresses you send mail to from any account.
- The other direction. The native program sends the add-on the AI app's requests: for example search terms, message ids, and the recipients and text of a draft. When a draft has attachments, the native program reads those files from your attachment folder and passes them to the add-on.
- Settings. Besides tool results, the add-on sends the native program two settings: which tools are turned on, and the path of your attachment folder. The native program tells the add-on the name each AI app gives itself, for the activity log. On the setup page, the native program reports which supported AI apps it found on the computer.
- The access key. Each time it starts, the native program makes a new random access key and keeps it, with its port number, in a file in your user's configuration folder that only your user can read. When Thunderbird closes, the native program removes the port and key from the file where it can (on Windows, Thunderbird may end it first). AI apps that start the native program with its connect command, whether MCP for Thunderbird set them up or you did, read the key from that file. An app that connects over HTTP gets the key only if you copy it from the options, and needs it copied again after each Thunderbird start.
- AI app vendors. What an AI app's vendor receives, keeps and uses is set by that vendor, not by MCP for Thunderbird. Read your AI app's privacy policy before connecting it to your mail.
- Noiz and the authors. Neither receives any of your data: MCP for Thunderbird has no server, no account and no update service of its own. It makes no network connections beyond your own computer (127.0.0.1); Thunderbird keeps talking to your mail servers as it always does.
- Sending mail. If you turn on direct sending, a message an AI app sends goes through your own mail account in Thunderbird, to the recipients you allowed, as if you had sent it yourself. Direct sending is off unless you turn it on.

What is stored on your computer

- In Thunderbird (the add-on's own storage in your profile): your settings (the accounts you ticked, the tool groups, the direct-sending list of addresses and domains you wrote, the attachment folder and the excluded folders, and for each account with excluded folders the paths of its folders seen so far, so that a folder renamed outside Thunderbird stays hidden) and the activity log. The activity log keeps the last 500 requests: time, AI app name, tool, the ids of the messages or the folder involved, and the outcome. It never records message text, and records no addresses as such; but a message id is an encoded form of the message's Message-ID header, which often contains a domain name, and a folder path can contain a name. You can clear it from the options.
- In your user's configuration folder: the native program's connection file, with its port, access key, process number and the time that process started. Once Thunderbird has closed, the port and key are removed where the native program had the chance, and are never used again either way.
- In your attachment folder: attachments that AI apps saved. They stay until you delete them.
- In your AI apps' settings: if you asked MCP for Thunderbird to set up an AI app, an entry named mcp-for-thunderbird that starts the native program. A backup of each settings file is kept next to it before it is changed.
- Logs: the native program logs only when it starts and stops (with the add-on's and Thunderbird's version numbers), when AI apps connect, and errors. It logs no message text, subjects or addresses.

Removing the add-on deletes its storage. INSTALL.md (https://github.com/wadejbeckett/mcp-for-thunderbird/blob/main/INSTALL.md#uninstalling) shows how to remove the native program, its connection file and the AI app entries.

Permissions the add-on asks for

Thunderbird describes these in its own words when you install the add-on. Each is used only for the reason given.

- accountsRead: Listing the accounts you can enable, and their folders.
- messagesRead: Searching and reading messages and their attachments.
- messagesMove: Moving, copying, archiving and moving to Trash. MCP for Thunderbird never deletes mail for good.
- messagesUpdate: Marking as read or flagged, and adding or removing tags.
- messagesTagsList: Listing your tags and finding them by name.
- messagesImport: Saving drafts into your Drafts folder, with the threading of replies and forwards kept.
- compose: Opening a filled-in compose window for you to check and send.
- scripting: Putting the text at the top of a compose window it opened, so the signature and its images stay as Thunderbird laid them out.
- addressBooks: Looking up contacts, only when the contacts group is on. MCP for Thunderbird does not change contacts.
- nativeMessaging: Talking to the native program.
- storage: Your settings and the activity log.
- messages.send (optional): Direct sending. Thunderbird asks you for it only when you turn on direct sending in the options, and it is not used otherwise.

Thunderbird 140 ESR does not know messages.send and ignores it. There MCP for Thunderbird offers neither mail_draft nor mail_send, which it offers only on Thunderbird 153 or later, and the options page keeps direct sending off.

Your choices

- Choose which accounts AI apps may use, and turn tool groups on or off, in the add-on's options.
- Exclude folders that AI apps must never see. On Gmail the same message also appears in All Mail, Important and Starred, so exclude those too; SECURITY.md (https://github.com/wadejbeckett/mcp-for-thunderbird/blob/main/SECURITY.md#known-limits) explains why.
- Pause every request from the toolbar button.
- Rotate the access key from the options. From then on, requests that use the old key are refused.
- Remove the add-on and the native program at any time.

Changes to this policy

Changes are published in PRIVACY.md in the project's repository (https://github.com/wadejbeckett/mcp-for-thunderbird/blob/main/PRIVACY.md), with a new date at the top. A change that sends any data somewhere new will be stated in the release notes of the version that makes it.

Contact

Questions about this policy: open an issue on the GitHub repository (https://github.com/wadejbeckett/mcp-for-thunderbird/issues). For a security problem, follow SECURITY.md (https://github.com/wadejbeckett/mcp-for-thunderbird/blob/main/SECURITY.md) instead.

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MCP for Thunderbird 0.3.1

by Wade John Beckett

About this Add-on

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Version 0.3.1 Released نومبر 4, 2026 124.8 KiB Works with Thunderbird 140.0 and later

Add-ons

Welcome to Thunderbird Add-ons.

On the go?

MCP for Thunderbird 0.3.1

by Wade John Beckett

About this Add-on

Version Information

Version 0.3.1 Released نومبر 4, 2026 124.8 KiB Works with Thunderbird 140.0 and later

Privacy Policy

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