Dynamic Undeniable Fair Certified Email with DDoS Protection

Fair certified email is an email system which employs the fair exchange protocol. All existing approaches to fair certified email achieve the fair exchange property between a single sender and a receiver only. But they do not offer the fair exchange between all senders and a receiver. So, a malicious receiver can deny receiving messages from some senders but do receive messages from other senders. Also, the existing certified email protocols do not prevent the distributed denial of service attack by malicious senders. We propose a new certified email protocol which provides the fair exchange for all senders, called the undeniable fairness, and distributed denial of service protection.