# SPF Checker

Inspect SPF records, expand bounded include trees, estimate DNS lookup terms and review compatible flattening options. Not a sender-IP evaluation.

Canonical: https://tamperbox.dev/spf-checker

Reviewed: 2026-10-13

## Capabilities and processing

Enter a domain or paste an SPF record. A domain is sent to our server, which reads its public TXT records and follows includes and redirects within its inspection limits. A pasted record is read in your browser; its includes are looked up the same way.

The result estimates lookup-causing terms against the SPF limit of 10, shows the include tree with the cost of each branch, flags void lookups, duplicate records, ptr, +all and typos, and proposes a flattening plan: which includes to replace with their IP ranges, the lookups left afterwards, and the record split into TXT strings.

## Example workflow

The page opens on harbor-supply.example, a sample domain that needs 11 lookups. Open the plan to see which includes to flatten, copy the record, or use Heal it to apply a repair.

## Limits and interpretation

A flattened record goes stale when a provider changes its ranges; re-check after provider changes. Macros are not expanded. Lookup counts follow RFC 7208: include, a, mx, ptr, exists and redirect count; ip4, ip6 and all do not. The application does not persist tool inputs or results.

The count is a bounded static expansion, not an SPF evaluation for a sender IP. Inspection stops after 100 nodes or 11 include levels. Address mechanisms and sender-dependent macros are not expanded. An earlier match can finish before the lookup limit. Flattening is offered only for fully inspected, compatible branches, with replacements kept in their original order.

## Related tools

[DMARC Checker](https://tamperbox.dev/dmarc-checker) inspects the domain policy. [Email Header Analyzer](https://tamperbox.dev/email-header-analyzer) reads the SPF result reported for a message.

[All tools](https://tamperbox.dev/) · [Privacy](https://tamperbox.dev/privacy)

## References

[Sender Policy Framework: RFC 7208](https://www.rfc-editor.org/rfc/rfc7208).