Gmail 5.7.26: unauthenticated mail rejected
Gmailauth_failureaction: fix_config
Gmail 5.7.26 means the message failed authentication. Gmail requires bulk senders to pass SPF or DKIM with domain alignment, and this message did neither. Retrying will not help. Fix the authentication and resend.
What it looks like in the log
550-5.7.26 This message does not have authentication information or fails to pass authentication checks.550-5.7.26 Unauthenticated email from <domain> is not accepted due to domain's DMARC policy.Why it happens
- No SPF record, or the sending IP is not authorised by it.
- DKIM not signing, or signing with a selector whose public key is missing or malformed.
- SPF and DKIM pass but neither aligns with the From domain, so DMARC still fails.
- The domain publishes a DMARC policy of quarantine or reject and the message did not satisfy it.
What to do
- Confirm the sending IP is covered by SPF, and that the record stays inside the 10 DNS-lookup limit.
- Confirm DKIM signing is on and the selector resolves with a valid public key.
- Check alignment: the domain that passes SPF or DKIM has to match the From domain, relaxed or strict as the policy requires.
- Read your DMARC aggregate reports for the sending source rather than guessing which leg is failing.
Related
Domain check audits the authentication this refusal names. Open domain check