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Yahoo TS errors: a temporary deferral

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Soft bounceYour sending reputationYahoo / AOL

The error

421 4.7.0 [TS01] Messages from 1.2.3.4 temporarily deferred due to unexpected volume or user complaints

421 4.7.0 [TS03] All messages from 1.2.3.4 will be permanently deferred

What it means

Yahoo returned a TS-prefixed error, which it documents as a temporary problem. Your server should retry automatically and the mail is not lost. Yahoo publishes TS as a family and does not define individual members, so the specific number does not carry a documented meaning.

The receiver is refusing your mail because of how your sending IP or domain behaves, not because of this particular message.

Why it happens

Yahoo defers rather than blocks when it is unsure about a sender — typically new IPs, sudden volume increases, or a rising complaint rate. Sustained deferrals are a warning that a block is coming.

How to fix it

  1. Let your queue retry; do not resend manually in a loop.
  2. If deferrals persist for more than a few hours, treat it as a reputation signal rather than a glitch.
  3. Check your complaint rate and enrol in Yahoo's Complaint Feedback Loop.
  4. Make sure SPF, DKIM and DMARC are all in place — Yahoo weighs authentication heavily.

Official documentation: Yahoo: SMTP error codes.

Related guides

  • 4.7.0: temporarily refused on policy grounds — The receiver is temporarily refusing your mail for policy reasons — most often rate limiting, greylisting, or a TLS requirement that was not met.
  • Gmail 4.7.28: temporarily rate limited — Gmail has seen an unusual volume from your IP and is throttling it. This is temporary and the mail is not lost — your server should retry.
  • 550 5.7.1: refused on policy grounds — The receiver refused to deliver the message for policy reasons. 5.7.1 is the most overloaded code in email — it covers authentication failures, relaying denials, blocklists, content rules and DMARC rejections.