What does Domain Keys Identified Mail (DKIM) use to verify that an email message was sent from an au

What does Domain Keys Identified Mail (DKIM) use to verify that an email message was sent from an authorized mail server?

A. Public Key Cryptography
B. Sender Policy Framework
C. Private Key Cryptography

D. Domain Name Service

Reference: https://help.symantec.com/cs/SMG_10_6_6/SMG/v5748156_v125807409/Sender-Authenticationemail_firewall_sender_authentication?locale=EN_US