# Yahoo 421 / 451 TS errors: message temporarily deferred

URL: https://iblockspam.com/smtp-errors/yahoo-421-ts-deferred
Last updated: 2026-10-09

Code: 421 (temporary failure, the sender retries)
Provider: Yahoo / AOL

Yahoo is temporarily deferring your mail, typically because of user complaints, spam-like content, poor IP reputation or unusual traffic. Your server should retry.

Yahoo's Sender Hub says a 421 or 451 error is a temporary problem, and lists reasons: unusual traffic patterns from your sending IP, spam characteristics in the message, complaints from Yahoo users, busy Yahoo mail servers, dynamic deprioritization after other suspicious behavior, an unavailable name server, or authentication results that couldn't be determined because of a temporary error.

Errors marked with a code beginning "TS" fall under Yahoo's "Message temporarily deferred" heading. Yahoo says the deferral may be due to substantial complaints from Yahoo users, objectionable or spam-like content, a poor reputation for the IP (or its subnet), or unusual traffic patterns. Your server may retry automatically later.

Yahoo asks senders to follow its Sender Requirements & Recommendations, review outgoing messages, and, if you don't primarily send bulk mail, examine your outbound queues to make sure spammers aren't abusing your server. If you keep seeing the same error over an extended period, Yahoo suggests submitting a Sender Support Request with the error details and diagnostic codes from your logs.

## Common causes

- Complaints from Yahoo users about your mail.
- Content Yahoo sees as spam-like.
- A poor reputation for your IP address or its subnet.
- Unusual traffic patterns, such as a sudden spike in volume.

## How to fix it (sender)

- Let your server retry; don't increase volume while deferred.
- Check outbound queues and accounts for abuse if you don't send bulk mail.
- Authenticate with SPF and DKIM (bulk senders need SPF, DKIM and DMARC) and send only to people who opted in.
- If it lasts, submit a Sender Support Request to Yahoo with the full error from your logs.

## How to fix it (recipient or admin)

- No action needed at Yahoo; the sender has to address the deferral.

**Q: Will Yahoo deliver my message after a TS deferral?**
It may. Yahoo describes TS errors as temporary and says your mail server may retry later. If the cause persists, retries keep failing until your server gives up.

**Q: How long should I wait before contacting Yahoo?**
Yahoo suggests submitting a Sender Support Request if you see the same error consistently over an extended period. In its guidance on complaint-related errors, it also asks administrators to review outgoing mail if an error lasts more than 48 hours.

Sources:
- SMTP Error Codes (Yahoo Sender Hub): https://senders.yahooinc.com/smtp-error-codes/

---

Source: iBlockSpam, https://iblockspam.com/smtp-errors/yahoo-421-ts-deferred (this is a Markdown copy; the HTML page is canonical). Quote with attribution and a link. Site index for AI assistants: https://iblockspam.com/llms.txt