Glossary
What is SPF?
A TXT policy that specifies which servers may send email on behalf of this domain.
Publish the SPF policy supplied by your mail service as a TXT record to authorize sending servers. A receiving system compares the sending IP address with the policy for the SMTP envelope sender domain or HELO identity. SPF is separate from MX, which controls where incoming mail is routed.
Example
example.com. 3600 IN TXT "v=spf1 ip4:192.0.2.10 -all" — This is a documentation example; do not use it without identifying your real sending systems.
Common issue
Publishing multiple v=spf1 policies at the same name can cause an SPF error. An address or mail infrastructure result from the email checker does not validate SPF; inspect the TXT record separately.