Yahoo Mail 421 4.7.0 [TS03]: reputation hold.

Traffic is temporarily held while Yahoo reviews a potential abuse signal.

How to fix 421 4.7.0 [TS03].

Retrying or final
Retrying
A 4xx reply. Your server keeps the message queued and tries again.
Who is at fault
Sender
Your authentication, reputation, content, or sending pace.
Severity
WarningTemporary Deferral
Temporary421 4.7.0 [TS03]

TS03 is triggered by spikes in unknown users, sudden content changes, or infrastructure anomalies that resemble abuse.

Next steps

  1. 1Audit recent creative, link domains, and sending speeds for big shifts.
  2. 2Ensure bounce processing removes invalid Yahoo addresses immediately.
  3. 3Confirm no other teams or systems are sending through the same IPs.
  4. 4Resume at a slower pace after the issue is corrected.
Yahoo Mail documentationEvery raw SMTP 421 reply

The same code at other providers.

Providers word the same code differently. Their fixes differ too.

421 4.7.0GmailTemporary system problemRetrying
421 4.7.0Microsoft 365 / OutlookTemporary system problemRetrying
421 4.7.0SFRToo many errorsRetrying

More Yahoo Mail codes.

Full Yahoo Mail playbook

Other Yahoo Mail fixes

421 4.7.0 [TSS04]Temporary deferralRetrying
421 4.7.0 [TS01]New or cold IP throttleRetrying
421 4.7.0 [TS02]Complaint rate deferralRetrying
451Unresolvable from domainRetrying
554Unresolvable from domainFinal
554Unresolvable return pathFinal

In the glossary

Bounce (Soft)A soft bounce is when an email fails to deliver for a temporary reason, like a full inbox or a short outage at the recipient mail server. The address is still valid, and the email may be delivered if you try again later.
DeferralA deferral is when a receiving email server temporarily refuses a message but suggests trying again later.
ThrottlingThrottling is when inbox providers or your email platform slow or limit how many emails you can send in a set time. It acts like a speed limit so big sends do not overwhelm their systems or hurt your reputation.
GreylistingGreylisting is an anti-spam technique where a receiving server temporarily rejects emails from unknown senders to test if they are legitimate.

Browse all raw Yahoo Inc replies →

More references.

SMTP field manual.

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