Frequently asked questions
What is an SPF record?
SPF (Sender Policy Framework) is a DNS TXT record that lists the mail servers authorized to send email for your domain. When a receiving server gets an email, it checks the sender's SPF record to verify the message came from an authorized server. This helps prevent email spoofing and improves deliverability.
What is the 10-lookup limit?
RFC 7208 limits SPF evaluation to 10 DNS lookups. Mechanisms like include, a, mx, ptr, exists, and the redirect modifier each count as one lookup. Mechanisms like ip4, ip6, and all do not require DNS lookups. Exceeding the limit causes a PermError, meaning your SPF record will fail validation entirely.
What does the all mechanism do?
-all (hard fail) rejects mail from unlisted servers — this is the recommended setting. ~all (soft fail) marks unlisted mail as suspicious but still delivers it. ?all (neutral) provides no protection. +all (pass) allows any server to send as your domain — this is dangerous and should never be used.
Why is the ptr mechanism deprecated?
The ptr mechanism requires a reverse DNS lookup for every connecting IP, which is slow and unreliable. RFC 7208 Section 5.5 explicitly discourages its use. Replace it with ip4, ip6, a, or mx mechanisms instead.
Can I have multiple SPF records?
No. RFC 7208 requires exactly one SPF record per domain. If multiple SPF TXT records are found, receivers will return a PermError. If you need to authorize additional senders, add them to your existing SPF record using include: mechanisms.
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