proton-safe-mcp

# Proton Safe MCP

<!-- mcp-name: io.github.fbossiere/proton-safe-mcp -->

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<img width="1774" height="887" alt="Proton Safe MCP — draft-only email tools, human-approved" src="https://raw.githubusercontent.com/fbossiere/proton-safe-mcp/main/docs/assets/proton-mcp-safe.png" />

A client-agnostic [FastMCP](https://gofastmcp.com) server for Proton Mail through the official [Proton Mail Bridge](https://proton.me/mail/bridge). It can read and search mail and create **drafts with attachments**. It deliberately **cannot send email** — you review every draft in Proton Mail and press Send yourself.

The server runs locally over STDIO for any MCP-compatible client (Claude Desktop, Claude Code, or anything else that speaks MCP). Received PDF, TXT, and CSV attachments can be inspected through bounded text extraction without exposing their raw bytes. Outgoing attachments are uploaded as bounded base64 chunks, so the server never receives or reads a client filesystem path.

Read the [full documentation](https://fbossiere.github.io/proton-safe-mcp/) for setup, configuration, tool inputs, security boundaries, and troubleshooting.

## Why "safe"?

Email is attacker-controlled input. Any sender can put adversarial instructions in a message body, and an AI agent that reads mail *and* holds write-capable tools is one prompt injection away from doing something you did not ask for. This project limits the blast radius by construction:

- **No send.** There is no SMTP client and no `send_message` tool in the codebase — a test asserts it.
- **No delete, no move,** and no raw received-attachment download tool.
- **Human in the loop.** Draft creation requires explicit confirmation of the exact content in the conversation, and Proton Mail still requires manual review and sending.
- **No filesystem access for clients.** Attachment bytes are streamed in chunks with declared size and SHA-256 verification; paths are rejected.
- **Loopback only.** STDIO transport, no listening socket, and the Bridge host is hard-coded to `127.0.0.1`.

These controls reduce risk but do not make email trusted. Never expose unrelated write-capable tools in the same unattended agent workflow.

## Architecture

![Architecture diagram showing an MCP client connected over STDIO to proton-safe-mcp, which uses loopback-only IMAP to create confirmed drafts in Proton Mail, where the user reviews each draft and presses Send](https://raw.githubusercontent.com/fbossiere/proton-safe-mcp/main/docs/assets/architecture.png)

## Security properties

- STDIO only: the server opens no listening network socket.
- Proton Bridge host is hard-coded to `127.0.0.1` (`PROTON_BRIDGE_HOST` is intentionally unsupported).
- No SMTP client, send tool, delete tool, move tool, or raw received-attachment download tool.
- Message and attachment reads use `BODY.PEEK`; attachment inspection returns bounded extracted text,
  metadata, and a SHA-256 digest, never raw bytes or files.
- Attachment input is chunked base64 with declared size and SHA-256 verification.
- Only PDF, DOCX, XLSX, PPTX, TXT, CSV, PNG, and JPEG uploads are accepted.
- Attachment tokens are random, short-lived, single-use, and reverified before draft creation.
- Draft creation requires an explicit client assertion that the user confirmed the exact recipients, subject, body, and attachments in the conversation.
- The Bridge-generated IMAP password is stored in the operating-system keyring.
- Draft bodies are stored as plain text plus a server-generated HTML alternative that
  HTML-escapes the confirmed body, so quoted markup can never be rendered.
- Recipient, subject, and folder inputs are validated against header/criteria injection.
- State files are private to the Unix account (`0700` directories, `0600` files, `O_NOFOLLOW`).

## Requirements

- Linux with the official Proton Mail Bridge installed, signed in, and running (developed and tested on Ubuntu).
- A Proton plan that supports Bridge.
- Python 3.11 or newer.
- [`uv`](https://docs.astral.sh/uv/).
- A working Secret Service keyring (`gnome-keyring` or compatible).

## Installation

Install the reviewed release from PyPI with [`uv`](https://docs.astral.sh/uv/):

```bash
uv tool install proton-safe-mcp==2.0.2
```

For development from source instead:

```bash
git clone https://github.com/fbossiere/proton-safe-mcp.git
cd proton-safe-mcp
uv sync --extra dev
```

Set the Proton address and Bridge IMAP port in the MCP process environment. No credential is
ever set here:

```bash
export PROTON_BRIDGE_USER="your-address@proton.me"
export PROTON_IMAP_PORT="1143"
```

To draft as another Proton address of the same account, add the optional sender allowlist in that
same environment, as comma-separated bare addresses:

```bash
export PROTON_BRIDGE_ALIASES="billing@example.com,legal@example.com"
```

Store the **Bridge-generated IMAP password** (shown in the Bridge UI), not your Proton account password:

```bash
proton-safe-mcp setup
```

The value shown by Bridge is installation-specific and works only against the local Bridge.

## Register with an MCP client

Configure a local STDIO server with these logical fields. Use `command -v proton-safe-mcp`
to obtain the absolute command path when your client does not inherit your shell `PATH`:

```json
{
  "name": "proton-safe",
  "transport": "stdio",
  "command": "/absolute/path/to/proton-safe-mcp",
  "args": ["serve"],
  "env": {
    "PROTON_BRIDGE_USER": "your-address@proton.me",
    "PROTON_IMAP_PORT": "1143"
  }
}
```

`PROTON_BRIDGE_ALIASES` goes in the same `env` block when a draft may use more than one From
address. See [Sender addresses](https://fbossiere.github.io/proton-safe-mcp/configuration/#sender-addresses).

Do not put `PROTON_BRIDGE_PASSWORD` in the client configuration. The server reads it from the OS keyring established by `setup`.

Copy-paste instructions are available for [Claude Code, Cursor, and VS Code](https://fbossiere.github.io/proton-safe-mcp/clients/).
AI coding agents can follow the safety-constrained [`llms-install.md`](llms-install.md) guide.

Verify the complete local setup without printing credentials, addresses, or mailbox data:

```bash
proton-safe-mcp doctor
```

## OpenAI plugin

The repository includes a private, local-first **Proton Safe** plugin for ChatGPT and Codex. It
packages safety-focused mail review and draft workflows with the same restricted MCP server:

- ChatGPT desktop and Codex can launch the bundled STDIO configuration directly on the Bridge
  machine, with no tunnel or dedicated server;
- direct MCP registration remains available when the packaged workflow skills are not needed;
- ChatGPT web or a client on another machine can optionally reach the Bridge host through OpenAI
  Secure MCP Tunnel without an inbound port;
- a remote deployment still keeps `proton-safe-mcp` and Proton Mail Bridge together, with IMAP
  fixed to `127.0.0.1`.

See the [OpenAI plugin guide](https://fbossiere.github.io/proton-safe-mcp/openai-plugin/) for local
ChatGPT desktop/Codex installation, direct MCP registration, and the optional remote tunnel.

> **Plugin installed but no Proton tools?** The bundled MCP configuration forwards
> `PROTON_BRIDGE_USER` and `PROTON_IMAP_PORT` from the environment that started Codex; it does not
> define their values. On Ubuntu, a correct `~/.config/environment.d/*.conf` file can still require
> a user-manager reload, while GNOME and already-running terminals can keep their earlier
> environment. If a menu relaunch still has no tools, start ChatGPT once from a terminal that has
> loaded the file. That terminal launch is a diagnostic, not a requirement for every start; the
> troubleshooting guide also provides a persistent per-user menu launcher. Follow the privacy-safe
> [Ubuntu recovery procedure](https://fbossiere.github.io/proton-safe-mcp/troubleshooting/#plugin-is-installed-but-mcp-shows-no-proton-tools)
> or the [FAQ](https://fbossiere.github.io/proton-safe-mcp/faq/) before reinstalling anything.

> **Help test the onboarding.** Linux and Proton Mail Bridge users can run the
> [10-minute external test](https://fbossiere.github.io/proton-safe-mcp/external-testing/) and
> submit privacy-safe [installation feedback](https://github.com/fbossiere/proton-safe-mcp/issues/new?template=installation-feedback.yml).

## Available MCP tools

| Category | Tool | Notes |
| --- | --- | --- |
| Read-only mail | `mailbox_status` | Bridge connectivity + INBOX counts |
| | `list_folders` | |
| | `list_sender_addresses` | The fixed From allowlist a draft may use |
| | `list_messages` | Never marks messages as read |
| | `search_messages` | Injection-safe IMAP `TEXT` search |
| | `read_message` | Bounded plain text; no attachment bytes |
| | `extract_attachment_text` | Bounded PDF/TXT/CSV text; no raw bytes or files |
| Attachment staging | `begin_attachment_upload` | Declares filename, type, size, SHA-256 |
| | `upload_attachment_chunk` | Ordered base64 chunks |
| | `finish_attachment_upload` | Verifies hash, returns single-use token |
| | `discard_attachment` | |
| Drafts | `create_confirmed_draft` | Requires exact conversational confirmation |

There is deliberately no `send_message` tool.

## Attachment and draft workflow

The