Error: "421 4.7.1 [TS03] All messages from x.x.x.x permanently deferred" when sending email to Yahoo

Learn why this delivery failure error may occur (where x.x.x.x is your IP address) when you’re sending email messages to Yahoo.

This message indicates Yahoo is seeing a high volume of emails from your IP address, which is a characteristic of unsolicited, bulk emailing.

  • We don't recommend resending until you check your subscription practices and lists to ensure that messages are sent only to users who've requested it.
  • If you're not the administrator of the mail server in question, we suggest that you contact the administrator.
  • If you're an administrator for message content or mailing policy and you've deployed significant changes or you've received this error for more than 48 hours, we ask that you review outgoing messages for objectionable content or practices.
    - See Yahoo’s best practices for senders for more information and note that we don't disclose further information about our filtering practices.
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