DomainKeys Identified Mail (DKIM) is a signature/cryptography-based email authentication that provides a method for validating a message during its transfer over the Internet. By validating that the message comes from the source it is claiming, IMSS provides spam and phishing protection for your network. Validated messages are not marked as spam and are not scanned for spam. This means false positives are reduced as is the need for scanning messages from a source that is known to be safe.