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, IMSVA 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.