A void lookup is an SPF DNS query that returns an empty answer, specifically an NXDOMAIN (the name does not exist) or a NOERROR response with no matching records. It happens during SPF evaluation when a mechanism such as a, mx, include, ptr or exists points at a host or domain that has no relevant DNS data.
RFC 7208 places a cap on these. A receiver may stop processing and return a PermError once it encounters more than two void lookups while evaluating a single SPF record. This protects DNS infrastructure from being abused for amplification through deliberately broken records.
Void lookups usually creep in when a third-party sender is removed but its include is left behind, when an mx mechanism references a domain with no MX records, or when a typo points at a non-existent host. The effect is that legitimate mail can suddenly start failing SPF and, by extension, DMARC alignment.
To check, evaluate your SPF record with a validator that counts void lookups and flags dead includes. Removing stale or mistyped mechanisms is the fix. Keeping the record tidy avoids both void-lookup failures and the wider PermError trap.
Check it on your domain
- SPF Checker: validates SPF and counts DNS lookups against the limit of 10.
- DNS Record Checker: looks up any DNS record type for a host.