Gmail authentication rejection

Fix Gmail 550 5.7.26

Gmail `5.7.26` is not one configuration defect. The reason text can identify unauthenticated mail, an SPF hard-fail branch or a DMARC-policy branch. Keep these paths separate before changing DNS.

Problem description

Gmail rejects mail from your domain with the following error message:

Gmail rejected: 550 5.7.26 Unauthenticated email is not accepted.

Classify the Gmail authentication error

How MailFixIt separates the branches

Unauthenticated mail: collect current message headers and identify which authentication result the receiver reports.
SPF hard-fail: evaluate the actual sending IP and envelope MAIL FROM domain, not merely the visible From domain.
DMARC-policy rejection: inspect the current applicable DMARC record and then validate SPF/DKIM alignment with fresh message evidence.

What the classification means

The branch is receiver-reported context only. A DNS match cannot prove an email's signature, historical DNS state, sender reputation or inbox placement. The checker therefore preserves the distinction between confirmed public-DNS defects, unknown results and message-path investigation.

Technical references: Gmail SMTP errors and RFC 7208 SPF.