What is SPF?

SPF (Sender Policy Framework, RFC 7208) is a DNS TXT record at your domain's root listing the IP addresses/ranges and included third-party services authorized to send mail claiming your domain in the SMTP envelope (MAIL FROM). A receiving server looks up that record and checks whether the connecting IP is on the list.

SPF alone does not stop spoofing of the visible From: header a recipient sees — that's what DMARC's alignment requirement adds on top.

If the health check reports "no SPF record found": add a TXT record at your domain's root listing your legitimate sending sources, ending in an all qualifier. A minimal starting point for a domain that only sends through its own mail server: v=spf1 mx -all — authorizes whatever your MX record points to and hard-fails everything else. Add an include: for each third-party sender (e.g. include:_spf.google.com for Google Workspace), staying mindful of the 10-lookup limit.