proton-mcp-unofficial

A Model Context Protocol server that lets an LLM read and send email through Proton Mail Bridge.

Unofficial. This is a community project and is not affiliated with, endorsed by, or supported by Proton AG.

Proton Mail is end-to-end encrypted and has no plain IMAP/SMTP API. Proton Bridge is Proton's official desktop app that runs a local IMAP and SMTP server on your machine and transparently encrypts/decrypts traffic to Proton. This MCP server talks to that local Bridge:

• Reading & searching → Bridge's local IMAP server
• Sending → Bridge's local SMTP server

Prerequisites

1. A Proton Mail account (Bridge requires a paid plan).
2. Proton Mail Bridge installed, running, and signed in.
3. Node.js 18+.

Get your Bridge connection details

Open the Bridge app → select your account → Mailbox details. You'll see:

• Username — your Proton address (e.g. [email protected])
• Password — a Bridge-specific password (NOT your Proton login password)
• IMAP host/port — usually 127.0.0.1:1143 (STARTTLS)
• SMTP host/port — usually 127.0.0.1:1025 (STARTTLS)

Bridge uses a self-signed TLS certificate, so certificate verification is disabled by default in this server. To enable it, install the Bridge CA certificate (Bridge → Settings → "Install" / export the cert into your trust store) and set PROTON_BRIDGE_TLS_REJECT_UNAUTHORIZED=true.

Connect it to an MCP client

Claude Desktop / Claude Code

Add to your MCP config (claude_desktop_config.json, or via claude mcp add for Claude Code):

{
  "mcpServers": {
    "proton": {
      "command": "npx",
      "args": ["-y", "proton-mcp-unofficial"],
      "env": {
        "PROTON_BRIDGE_USERNAME": "[email protected]",
        "PROTON_BRIDGE_PASSWORD": "your-bridge-password"
      }
    }
  }
}

For Claude Code specifically:

claude mcp add proton \
  -e [email protected] \
  -e PROTON_BRIDGE_PASSWORD=your-bridge-password \
  -- npx -y proton-mcp-unofficial

Tools

| Tool | Description | | --- | --- | | list_mailboxes | List all folders with total/unread counts. | | list_messages | List recent messages in a mailbox (newest first). | | read_message | Fetch a full message (headers + body) by UID. | | search_messages | Search by from/to/subject/body/date/unread. | | mark_read | Add or remove the \Seen flag on a message. | | send_email | Send an email (to/cc/bcc, subject, text/html, from alias). | | list_addresses | List account addresses/aliases you can send from. |

Configuration

All configuration is via environment variables (see .env.example):

| Variable | Required | Default | Notes | | --- | --- | --- | --- | | PROTON_BRIDGE_USERNAME | ✅ | — | Your Proton address. | | PROTON_BRIDGE_PASSWORD | ✅ | — | Bridge-specific password. | | PROTON_BRIDGE_HOST | | 127.0.0.1 | | | PROTON_BRIDGE_IMAP_PORT | | 1143 | | | PROTON_BRIDGE_SMTP_PORT | | 1025 | | | PROTON_DEFAULT_ADDRESS | | = username | Default From when send_email omits from. | | PROTON_BRIDGE_ADDRESSES | | — | Comma-separated aliases list_addresses returns. | | PROTON_BRIDGE_FROM | | — | Legacy fallback for the default From address. | | PROTON_BRIDGE_TLS_REJECT_UNAUTHORIZED | | false | Set true after installing the Bridge CA. |

Security notes

• Credentials are read from environment variables only (set them in your MCP client config); nothing is written to disk. If you use a .env file, keep it out of version control.
• The server communicates only with your local Bridge — no third party sees your password or mail.
• send_email sends real email. Review what the LLM drafts before letting it send autonomously.

License

MIT