Certified Server Validation
Definition: Email authentication method that verifies the hostname of a client requesting an SMTP session as authorizing that client's IP address.
Certified Server Validation (CSV) provides a mechanism for a mail-receiving server to assess a mail-sending server. In particular, CSV permits a mail-receiving server to determine:
1. Whether a mail-sending host is correctly identifying itself. 2. Whether the operator of the sending host's network has authorized it to operate as a mail relay. 3. Whether independent parties have a good assessment of the quality of that network's mail operation.
CSV verifies only the relay initiating the "last hop" before the server doing the CSV check. This avoids problems with forwarding that plague other IP-based authentication methods.