What it is
SPF lets a domain publish which hosts may send SMTP mail using that domain in the envelope sender or HELO identity.
Why it matters
Receivers use SPF as one authentication signal and as one path to DMARC alignment. A broken record can make legitimate mail fail before content is considered.
How to implement
Publish exactly one TXT policy per domain. Authorize only current senders, stay within the ten DNS-lookup limit, and finish with a deliberate -all or ~all while rolling out.
Common mistakes
- Publishing multiple SPF records.
- Adding broad providers that do not send for the domain.
- Assuming SPF authenticates the visible
Fromaddress by itself.
Verification
Resolve the record from public DNS, count all recursive lookups, and inspect Authentication-Results on messages from every sending source.