Email delivery troubleshooting

Email errors and DNS problems, explained with evidence

Start with the error your receiver or provider reported. Each guide explains what the symptom means, what public DNS can verify, and how to make a reversible change. Then run MailFixIt's free diagnostic with your real domain and, when available, problem-message headers or bounce text.

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Gmail and Outlook rejection errors

Outlook 550 5.7.515Authentication requirements were not met. Gmail 550 5.7.26Message rejected as unauthenticated. Gmail 550 5.7.27SPF authentication failed. Gmail 550 5.7.30DKIM authentication failed. Gmail 550 5.7.40DMARC policy is required.

SPF troubleshooting

SPF missing on a subdomainCheck the exact bounce or MAIL FROM domain. SPF include after allFind mechanisms receivers never evaluate. SPF include has no recordRepair a missing provider dependency safely. SPF void lookup limitFind evaluated DNS dependencies with no answer.

DKIM verification

Amazon SES DKIM pendingCompare all three Easy DKIM CNAME records. Cloudflare DKIM CNAMECheck whether the required CNAME is observable. Invalid DKIM public keyDiagnose malformed or unusable key material. Microsoft 365 DKIM CNAMECompare the provider-issued owner and target.

DMARC policy and reporting

DMARC subdomain policyDetermine the effective policy for a subdomain. DMARC reports not receivedVerify external report-destination authorization.

Incoming mail, MX and DNS publication

DNS record not detectedFind wrong owner names, values or delegation. Email stopped after a DNS changeCompare MX routing with the intended provider. Null MX email rejectedDistinguish intentional no-mail from a conflict.

Amazon SES custom MAIL FROM

SES MAIL FROM not alignedInvestigate fallback and Return-Path mismatch. SES MailFromDomainNotVerifiedVerify the custom MAIL FROM MX record.

Use the guide, then check the real domain

Static examples explain a failure pattern. The free diagnostic resolves current public DNS and can use safe fields extracted from message headers or rejection text to select a more relevant scenario.

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