Release a quarantined email

MillionSend extension: delivers a held message to the inbox. Mail held before screening ran (not_allowlisted, unauthenticated_sender, failed_auth) is screened first when screening can run, and stays held when the judge scores it at 80 or more (409 held_by_screening); otherwise it is never screened again. trust_sender also adds the sender to the allowlist, only for mail held as not_allowlisted from a verified (external) sender. MCP connections release for an agent: never mail held for prompt injection, phishing, a virus or failed authentication (403 forbidden), and any other hold only once screening, run at every MCP release, scores it under 80; while screening can't run, nothing is released (503 screening_unavailable). Not for inbox-scoped keys.