Most common causes
- Recipient or policy condition is permanently rejecting the message
- Authentication, reputation or content policy blocks the delivery
- The detailed provider text identifies a specific permanent cause
What to verify next
- Read the complete 553/554 diagnostic
- Do not indefinitely retry a permanent failure
- Verify authentication and sender reputation when the text points to policy
- Correct the stated condition before retesting
Best diagnostic path
Live analysis
Mail Failure Doctor
Classify the complete rejection and preserve provider-specific diagnostic context.
Open analysis → Live analysisEmail Infrastructure Digital Twin
Map the domain’s public mail infrastructure and provider relationships before remediation.
Open analysis →Why the exact message matters
The same status family can be triggered by different conditions, and providers frequently add diagnostic text that narrows the issue. Use the complete rejection text rather than treating the numeric code as a complete diagnosis.
Provider reference
For the provider-defined meaning and current requirements, review Yahoo Sender Hub SMTP error codes.