1.7 Versioning and Capability Negotiation
This document covers versioning issues in the following areas.
Message versions: Two message versions, MAIL_REP_MSG_V1 and MAIL_REP_MSG_V2, are used by the DRS Protocol Extensions for SMTP.
Capability negotiation: There is no capability negotiation when the MAIL_REP_MSG_V1 message is used. The MAIL_REP_MSG_V2 message includes an explicit vector of capabilities. See section 2.2 for details.
Encryption and hashing algorithms: Two encryption and hashing algorithms are allowed, but there is no negotiation in the protocol to configure which to use in sending messages or to identify which are used when receiving messages. Therefore, two machines implementing this protocol which are configured to use different encryption and/or hashing algorithms can fail decryption and verification. See section 3.3.5.3 for details.