SPF
SPF (Sender Policy Framework) is a DNS TXT record listing the servers allowed to send mail for a domain, so receivers can reject mail from other sources.
How it works
The record starts with v=spf1 and lists mechanisms (ip4, include, a, mx) ending with ~all or -all. Receivers evaluate it against the envelope sender, and the evaluation is limited to 10 DNS lookups.
SPF alone does not protect the visible From address; DMARC alignment is needed for that.
How to protect yourself
- Keep the record under the 10-lookup limit and end it with -all once all senders are listed.
- Pair SPF with DKIM and an enforcing DMARC policy.