Protonmail-rs — Proton Mail MCP Server

Unofficial, pure-Rust Proton Mail client — library, CLI, and MCP server with end-to-end OpenPGP encryption. Gives AI agents secure, encrypted email capabilities through Switzerland's privacy-first email provider.

Detail	Value
GitHub	filippofinke/protonmail-rs
Language	Rust
Tools	MCP-native email operations
Transport	stdio
Stars	★1 (new — July 2026)
License	TBD

Why This Matters for Operators

Proton Mail is the leading encrypted email provider, used by 100M+ users worldwide — including journalists, legal firms, healthcare providers, and security-conscious businesses. This MCP server is the first to bring Proton Mail's end-to-end encryption to AI agent workflows:

• HIPAA/GDPR compliance: Encrypted email for regulated industries
• Legal communications: Attorney-client privileged email through AI agents
• Secure client onboarding: AI agents send encrypted onboarding documents
• Privacy-first operations: Zero-access encryption means not even Proton can read emails

Prerequisites

• Proton Mail account (free or paid)
• Proton Mail Bridge (for IMAP/SMTP access — paid plans only)
• Rust toolchain (for building from source)
• OpenPGP keys managed through Proton's key infrastructure

Installation

# Clone and build
git clone https://github.com/filippofinke/protonmail-rs.git
cd protonmail-rs
cargo build --release

# Binary at target/release/protonmail-rs

MCP Client Configuration

{
  "mcpServers": {
    "protonmail": {
      "command": "/path/to/protonmail-rs",
      "args": ["mcp"],
      "env": {
        "PROTON_API_URL": "https://mail.proton.me/api",
        "PROTON_SESSION_KEY": "your-session-key"
      }
    }
  }
}

Key Capabilities

Capability	Description
Read inbox	Fetch and decrypt emails with OpenPGP
Send encrypted	Compose and send end-to-end encrypted emails
Search	Search encrypted mailbox by subject, sender, date
Key management	Import/export PGP keys, verify signatures
Folder operations	List, create, move emails between folders
Labels & filters	Apply labels and manage sieve filters

CorpusIQ Use Case

Operators in regulated industries can use this MCP server alongside CorpusIQ's business connectors:

1. Secure document workflow: AI agent sends encrypted contracts (via Proton Mail) when DocuSign events complete
2. Compliance notifications: Agent sends encrypted audit logs to compliance officers
3. Client communications: Agent manages encrypted email threads for legal/financial clients
4. Privacy-first CRM: Combine with HubSpot connector for encrypted client communications

Security Considerations

• End-to-end encryption: Emails are encrypted client-side before transmission — the MCP server never sees plaintext
• Zero-access architecture: Proton Mail cannot decrypt your emails
• Session management: Use short-lived session tokens, not persistent credentials
• Audit trail: All agent-initiated email operations are logged in Proton Mail's activity log

Limitations

• Proton Mail Bridge required for IMAP/SMTP access (paid plans only, ~$4/month)
• Unofficial client — not maintained by Proton AG
• New project (July 2026) — expect API changes and limited tool coverage initially
• SRP authentication may require periodic re-authentication

Troubleshooting

Issue	Solution
Authentication failed	Regenerate session key via Proton web client → Settings → Security → Sessions
OpenPGP key not found	Verify key is uploaded to Proton's key server and public key is accessible
Rate limited	Proton Mail has per-account rate limits (~100 emails/day free, higher on paid)
Build fails	Ensure Rust toolchain is up to date: rustup update stable

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Discovered: July 1, 2026 · Source: GitHub (topic:mcp-server created >2026-06-30) Part of the CorpusIQ External MCP Server Catalog