SPF Record Validator & 10-Lookup Budget Tester
Validate Sender Policy Framework syntax, recursively trace include trees, and safeguard against the strict 10-lookup DNS limit.
How SPF Record Validator Works
TXT Record Extraction
Finds TXT records starting with `v=spf1` on the apex domain.
Recursive Include Expansion
Fetches nested SPF records referenced by `include:` mechanisms to compute true DNS cost.
PermError & Void Detection
Evaluates syntax flags, qualifiers (`~all`, `-all`), and ensures total DNS lookups stay ≤ 10.
RFC Engineering Standards
Every check performed by this tool adheres strictly to the Internet Engineering Task Force (IETF) Request for Comments:
- RFC 7208 (Sender Policy Framework)
- RFC 4408 (Legacy SPF Standard)
Common Issues & How to Fix Them
If our diagnostic discovers configuration anomalies, use the remediation steps below:
Remediation: RFC 7208 caps SPF lookups at 10. Exceeding this causes receiving servers to throw SPF PermError. Flatten your SPF record or remove unused vendor includes.
Remediation: A domain must only have exactly one SPF record. Merge multiple `v=spf1` strings into a single record.
Remediation: Consider moving to `-all` once SPF, DKIM, and DMARC alignment are verified.
Frequently Asked Questions
Why does RFC 7208 limit SPF lookups to 10?
To prevent Denial of Service (DoS) amplification attacks against DNS servers. If an SPF record requires more than 10 lookups, receiving mail transfer agents return a 'PermError' and treat the email as unauthenticated.
What is SPF flattening?
SPF flattening replaces dynamic `include:vendor.com` mechanisms with the vendor's actual static `ip4:` and `ip6:` CIDR blocks, reducing DNS lookups from many to zero.
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