Home/Fix/DNS & Infrastructure ProblemsDNS & Infrastructure ProblemsFix MX, PTR/rDNS, HELO, TTL, and authoritative DNS failures that affect email.Reading time: 8 minDifficulty: IntermediateEstimated duration: 8 minPrerequisites: DNSLast updated: 2026-07-17Author: EmpirePrerequisitesDNSDomain Name System — the lookup fabric email authentication depends on.▼Related learningDNSDomain Name System — the lookup fabric email authentication depends on.▼Related problemsCNAME at zone apexA CNAME is placed at the zone apex where other record types are also required.HELO / EHLO problemsThe SMTP HELO/EHLO hostname is missing, invalid, or inconsistent with reverse DNS.Inconsistent authoritative answersAuthoritative name servers for the same zone return conflicting data.Incorrect MX targetMX points to the wrong host name or unreachable mail server.Missing glue recordsDelegation references in-bailiwick name servers without required glue.MX record missingNo MX record is published for a domain that should receive mail.NXDOMAIN for expected nameA name that should exist returns NXDOMAIN from authoritative servers.Reverse DNS mismatchPTR (reverse DNS) for a sending IP is missing or does not match the forward hostname used in mail.Stale DNS cache after changeResolvers still serve prior answers after an authoritative change because TTL has not expired.Wrong TTL for cutoverTTL values are too high for a planned cutover, prolonging mixed old/new answers.▼Recommended toolsdigCLI DNS lookup utility for authoritative and recursive inspection of mail-related records.nslookupInteractive DNS lookup utility commonly used for quick MX and TXT checks.Google Admin Toolbox DigBrowser-based dig-style DNS lookup from Google’s Admin Toolbox.Google Admin Toolbox CheckMXGoogle Admin Toolbox Check MX for inbound mail DNS sanity checks.WorkflowsOpen step-by-step: Verify DNS recordsVerify zone authority, MX/address records, and authentication-related TXT publications.Open step-by-step: Diagnose mail DNS failuresSeparate authoritative errors, cache staleness, and delegation problems.Open step-by-step: Configure reverse DNSAlign PTR and HELO/EHLO for each sending IP before warmup or production volume.Continue LearningDelivery ProblemsTroubleshoot mail that is not delivered, delayed, deferred, or bouncing.PreviousDMARC ProblemsNextDelivery Problems