🛡️ RFC 7208 DNS Protocol Checker

SPF 10-DNS-Lookup Hard Limit Checker

Verify your SPF record inclusion depth and prevent fatal ‘PermError’ authentication dropouts.

Active Third-Party Services (Includes)
Additional MX & A Mechanisms 1 Lookup
Current Lookups
6 / 10
RFC 7208 total
Remaining Safe
4 Left
Before failure
Authentication Status
PASS
Valid SPF Syntax
PermError Risk
LOW RISK
<8 DNS queries
GENERATED SYNTHETIC SPF RECORD 6 of 10 Lookups Used 
v=spf1 include:_spf.google.com include:spf.protection.outlook.com include:_spf.autosmtp.io mx ~all

🛡️ Automated SPF Flattening & AutoSMTP Dedicated Nodes

AutoSMTP’s automated DNS engine flattens nested SPF includes into pure IP netblocks, eliminating PermErrors forever.

Understanding the RFC 7208 10-Lookup Hard Limit

To prevent Denial of Service (DoS) amplification attacks, RFC 7208 Section 4.6.4 mandates that receiving mail exchangers must abort SPF evaluation if resolving a record requires more than 10 DNS queries. Any record exceeding 10 lookups returns a fatal PermError.

Major mailbox providers like Google and Microsoft treat SPF PermError as an unauthenticated message, bypassing SPF alignment and causing messages to fail DMARC verification.