Baryon — Proton Mail via Bridge MCP server

Baryon MCP

A local, permission-limited bridge between Proton Mail and the AI you choose

Baryon connects an MCP-compatible AI assistant to Proton Mail through a local Proton Mail Bridge.

It lets your assistant search and read email, understand conversations, work with attachments, and prepare drafts for you to review. Baryon cannot send email, move or delete ordinary messages, or mark messages as read.

Baryon has no hosted service. You decide which MCP client and AI model receive your email content.

[!IMPORTANT]

Baryon and Proton Mail Bridge run locally, but your AI may not.

Email content requested through Baryon is returned to your MCP client and can be passed to the model it uses. With a local or self-hosted model, processing can remain on infrastructure you control, depending on your client configuration. With a hosted service, selected email content is sent to that provider.

For example, using Baryon with hosted Claude or Codex models sends requested email content to Anthropic or OpenAI infrastructure respectively. Review your client's and provider's privacy and data-retention terms before connecting it to your mailbox.

What you can do

• Find messages by text, sender, recipient, subject, date, or unread state.
• Read an email or an entire conversation.
• Inspect, retrieve, and save attachments.
• Prepare new messages as Proton Mail drafts.
• Review, edit, and send those drafts yourself in Proton Mail.

For example, you could ask your assistant:

Find the renewal notices I received this month and summarise the price changes.

Read my conversation with Alice and prepare a polite follow-up draft.

Find the PDF invoice attached to the latest message from Acme and save it locally.

Summarise this support thread and draft a reply covering the unresolved questions.

Useful access, deliberate limits

Replacing an existing draft saves its replacement before removing the previous draft copy. Baryon has no tool for deleting ordinary received or sent messages.

How it works

Proton Mail
    │
    ▼
Proton Mail Bridge       local
    │
    ▼
Baryon                   local
    │
    ▼
Your MCP client
    │
    ├── Local model      can stay on infrastructure you control
    │
    └── Hosted model     content is sent to its provider

Baryon talks only to Proton Mail Bridge on your computer. It refuses to send Bridge credentials to a non-loopback address and verifies Bridge using its exported TLS certificate by default.

Before you start

You will need:

• Proton Mail Bridge installed, signed in, and running.
• An MCP client that can launch local MCP servers over stdio.
• The IMAP username and generated password shown in Bridge's mailbox settings.
• Bridge's exported TLS certificate for a verified connection.

Use the password generated by Bridge, not your normal Proton account password. Export cert.pem from Settings → Advanced settings → Export TLS certificates in Proton Mail Bridge.

Installation

1. Install the binary

macOS:

brew install --cask combor/tap/baryon-mcp

Shortened. The full README is on GitHub.