To enable domain protection for the organization, the administrator must configure an outgoing mail policy that matches the sender and the from headers of the email. The sender header is the envelope sender address that is used by SMTP to route the email. The from header is the address that is displayed to the recipient as the source of the email. These headers are used to generate and verify a DomainKeys Identified Mail (DKIM) signature, which is a cryptographic method of validating the authenticity and integrity of an email message.

The other headers are not relevant for domain protection. The message-ID header is a unique identifier for each email message. The URL reputation header is a score that indicates the likelihood of a URL being malicious. The mail-from header is an alias for the sender header.