SPF (Sender Policy Framework) is a DNS TXT record that lists the servers allowed to send mail for a domain. Receivers check the connecting IP against that list during the SMTP transaction.
A correct example#
example.com. IN TXT "v=spf1 include:_spf.google.com include:sendgrid.net ip4:203.0.113.10 -all"Every element is there for a reason, and each maps to one of the setup steps below.
What good looks like#
- Done: Inventory every service that sends mail as your domain: your ESP, CRM, helpdesk, billing system, and internal mail server.
- Done: Collect each vendor's SPF include mechanism (for example include:_spf.google.com) from their documentation.
- Done: Publish one TXT record at the root of the domain starting with v=spf1, listing each include, then ending with ~all (softfail) while testing.
- Done: Verify with a lookup tool that the record resolves and stays under 10 DNS lookups and 255 characters per string.
- Done: Move to -all once DMARC reports confirm all legitimate sources pass.
What bad looks like#
- Seen in audits: Exceeding the 10-lookup limit, which causes a permerror and effectively disables SPF.
- Seen in audits: Publishing two SPF records on one domain; receivers treat this as a permanent failure.
- Seen in audits: Forgetting that SPF checks the Return-Path (envelope sender), not the visible From address, so forwarded mail often fails.
- Seen in audits: Using +all or leaving ?all in production, which authorizes everyone.
How to move from bad to good#
Work through the good list in order and re-verify after each change. Most teams find one or two items from the bad list already present; fixing those usually produces the largest improvement.
Frequently asked questions#
Does SPF alone stop spoofing?
No. SPF validates the envelope sender, which spoofers can set to their own domain while forging the visible From. DMARC closes that gap by requiring alignment.
What does ~all versus -all mean?
~all is softfail: receivers mark but usually accept. -all is hardfail: receivers may reject. Start with ~all, graduate to -all once DMARC data is clean.
How do I fix 'too many DNS lookups'?
Remove unused includes, replace includes with ip4/ip6 mechanisms where vendors publish static ranges, or use an SPF flattening service.