SPF, DKIM and DMARC

SPF (Sender Policy Framework) is a TXT record listing the servers allowed to send mail for a domain. DKIM (DomainKeys Identified Mail) adds a cryptographic signature to each message, checked against a public key published in DNS, so tampering shows. DMARC ties both to the visible From address and tells receivers what to do when checks fail (p=none to monitor, quarantine or reject) and where to send reports.

Since February 2024, Gmail and Yahoo have required SPF or DKIM from every sender, and all three, plus one-click unsubscribe on marketing mail, from anyone sending more than 5,000 messages a day to their users; Microsoft set similar rules for Outlook.com in 2025. Email services show the exact records to add when you verify a domain. Once DMARC is enforced, BIMI can show a brand logo beside messages in some inboxes.