- correct PTR record to ensure rDNS (reverse DNS) validation succeeds. (Required)
- SPF records for the sending domain, and the mail servers DNS name. (Recommended)
- DKIM records and configuration to sign the outgoing mail. (Recommended, but often poorly implemented.)
- DMARC records to allow receiving servers to apply your domains SPF and DKIM policies (Recommended, but not often used by smaller volume servers.)