It is not SMIME (Secure Multipurpose Internet Mail Extension): an extension of MME in terms of security. It can encapsulate MME entities (such as digital signatures and encrypted information) into secure objects. Enhance security services, such as the function of the recipient to confirm receipt, to ensure that the recipient can't deny the received mail. It can also be used to provide data confidentiality, integrity protection, authentication and authentication services. SMME only protects the message body and does not encrypt the header information, so that the message can be successfully delivered between the sender and the receiver's gateway.