A Multi-Level Security Framework for Email Communications This whitepaper proposes the Tiered Security Email Protocol (TSEP), a backward-compatible extension to SMTP that enables end-to-end encrypted email with graduated security levels. TSEP decouples identity and key management from email infrastructure by delegating authentication to third-party identity providers (banks, enterprise identity systems, consumer authentication apps). The protocol defines three security levels optimized for different use cases: cached-key mode for routine communications, online verification for sensitive messages, and time-bound verification for high-stakes transactions.