550 5.7.26
550 5.7.26 IPv6 or Guideline Violation
The message fails Google’s bulk sender guidelines—commonly IPv6, DNS, or authentication requirements.
Gmail returns 5.7.26 when an IPv6 sender is missing PTR records, when SPF/DKIM are absent, or when one-click unsubscribe headers are missing.
Severity
ERROR
Provider
Gmail
Reference
Mitigation Portal
Last Reviewed
2025-06-01
How to Fix 550 5.7.26
Follow these steps to resolve this Gmail SMTP error and restore normal delivery.
- ✓Publish forward and reverse DNS for each sending IP (especially IPv6).
- ✓Ensure SPF, DKIM, and DMARC all align with the visible From domain.
- ✓Add RFC 8058 one-click unsubscribe headers for promotional traffic.
- ✓Follow Google’s February 2024 checklist and document compliance.
Helpful Resources
More Gmail SMTP Codes
Keep these related troubleshooting guides handy while addressing 550 5.7.26.
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