A Hybrid PQC + Multi-Source-Enhanced Entropy Key-Distribution and End-to-End Encrypted Email Client

The threat of quantum computing to classical cryptographic systems rises the necessity for development of quantum resistant security framework for digital communication. Current email systems depend completely on these centralized architectures which are vulnerable to server breaches, while their cryptographic foundation and currently used encryption standards and protocols (RSA and ECC), will face existential crisis and risk from quantum algorithms like Shor's algorithm. To address these challenges, this paper presents a unified and intelligent quantum-resistant email security framework that integrates post-quantum cryptography with multi-source entropy-driven key generation for protecting emails and attachments. The proposed system employs lattice-based cryptographic schemes combined with AI-assisted randomness generation to enhance key unpredictability and resilience. Performance evaluation demonstrates a system efficiency of 90.32% with an effective 135-bit quantum-safe security strength, achieving a practical balance between performance and security with the framework ensuring true end-to-end encryption, guaranteeing that only authorized clients can access sensitive data even in the event of server compromise. Furthermore, the proposed approach provides a scalable foundation for future expansion into a comprehensive quantum-safe digital workspace incorporating secure collaboration tools, enhanced usability, and regulatory compliance.