Yahoo and AOL sender troubleshooting

Yahoo email bounce errors, grouped by the action they require

Yahoo's current Sender Hub groups SMTP failures by temporary deferral, permanent policy, RFC compliance, authentication, and recipient state. Use the complete response—not an old tag alone—to choose the correct guide.

Provider scope: Yahoo and AOL responses can contain changing diagnostic tags. These pages use stable intent canonicals and include old tags only when current first-party evidence supports them.

Temporary delivery responses

Message temporarily deferred421/451 or TS-family responses: retry with backoff and review traffic.

Permanent policy and format responses

554 Message not allowedBroad policy rejection requiring the full Yahoo reason.RFC headers rejectedRepair message generation and malformed headers.

Recipient responses

Yahoo user does not existConfirm or remove the invalid recipient.

How to use these guides

Keep the complete Yahoo response, timestamp, and sending-server log.
Choose the page by exact wording and ownership.
Follow provider support for reputation and policy decisions.
Do not change SPF, DKIM, or DMARC unless the response and evidence actually identify authentication.

Primary source: Yahoo Sender Hub SMTP Error Codes, reviewed September 8, 2026.