S/MIME is the abbreviation for Secure/Multipurpose Internet Mail Extensions, which is an international standard protocol based on PKI technology and used to sign and encrypt email body via digital certificate. The advantage is that the email is not only encrypted, but also signed with the sender’s real identity information verified by CA, so that the recipient can confirm the sender's real identity.
The PGP encryption method means the sender himself create the encrypting certificate to encrypt the email; there is no trusted identity information in the certificate, and it is only for encryption. MeSince® thinks that PGP is not suitable for eCommerce communication. It’s as important as email encryption to make sure of the sender’s real identity.
At present, the popular email client software such as Microsoft Outlook, Mozilla Thunderbird and Apple iMail all support S/MIME encryption. MeSince® uses S/MIME standard to sign and encrypt email so that any email client software that supports S/MIME can cooperate with MeSince for decrypting encrypted messages, just need to export the certificate and install it in other email client software.
NIST SP 800-177 “Trustworthy Email” Security Recommendation 5-4: Do not use OpenPGP for message confidentiality. Instead, use S/MIME with a certificate that is signed by a known CA. And Security Recommendation 4-11: Use S/MIME signatures for assuring message authenticity and integrity.