A DKIM signature for outgoing messages is a digital signature added to messages sent from email addresses of a certain domain for purposes of identifying users by the name of the corporate domain.
DomainKeys Identified Mail (DKIM) technology combines several existing anti-phishing and anti-spam methods to improve the quality of classification and identification of legitimate email. Instead of a traditional IP address, DKIM technology adds a digital signature associated with the name of the corporate domain to the message for the purpose of identifying its sender.