SPF void lookup
A void lookup is a specific category of SPF evaluation outcome, defined in RFC 7208 section 4.6.4, tracked separately from the record's overall 10-lookup budget: a DNS query during SPF evaluation that returns either a positive answer with an empty answer set, or a Name Error (NXDOMAIN). RFC 7208 recommends -- a SHOULD, not the hard MUST governing the 10-lookup cap -- limiting void lookups to 2 for the entire evaluation, so a record can't force a receiving server to keep querying names that plainly don't resolve. In practice the limit gets tripped by stale includes: a mechanism like include:oldvendor.com left in a record long after that vendor deleted its SPF record or let the domain lapse. Each one burns through the 2-void budget, and a third stale or missing name can turn the whole check into a PermError, the same outcome as exceeding the 10-lookup limit.
By AdminKit team, Netbase JSC · Updated