How does the SPF 10-lookup limit work technically?
What counts as a lookup:
- include: (one lookup, plus included record's lookups)
- a: (one lookup)
- mx: (one lookup per MX, plus A lookups)
- redirect= (one lookup)
- exists: (one lookup)
What does not count:
- ip4: and ip6: (no lookup, literal values)
- all (no lookup)
Recursive counting: include statements cause lookups of the included record, which may have its own includes.
Evaluation: Lookups counted during processing. If count exceeds 10, result is permerror. Authentication fails.
Example: 3 includes, each including 3 more = 3 + 9 = 12 lookups = permerror.
Limited number of cross-reference checks allowed. Exceed the limit and the verification process fails.
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