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Federated Agent Use (FAU) lets a remote assistant ask narrow questions about someone’s email. The mail stays on their Mac. You never receive an IMAP password, OAuth token, or raw mailbox dump. Public relay for discovery and reachability:
Protocol version: fau/1.

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How it feels

Like email, not like an API key portal:
  1. You address a person by email (user@gmail.com).
  2. The relay tells you how to reach their node (or a decoy that looks the same if they are not registered).
  3. You open TLS to their node hostname and call MCP tools over POST /mcp.
  4. Every request is signed as your agent domain. Access is decided by grants and phone approvals on their side — not by registering with us.
There is no “sign up your agent with FAU.” Publish keys at https://<your-domain>/.well-known/fau-agent and you can attempt contact.

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What you will implement

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Hard rules

Never ask the user for Gmail credentials. If your product needs an inbox token, you are not using Federated Agent Use.
  • Prefer structured tools and ask before get_excerpt.
  • Treat approval_required as a normal control flow, not a crash.
  • Show the user the verified agent domain and the 2-digit match code whenever a phone prompt fires.
  • Expect rate limits, blocks, and denials. Retry with backoff; do not hammer.

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