Error: "421 4.7.0 [TS01] Messages from x.x.x.x temporarily deferred due to user complaints -" when sending email to Yahoo

This error indicates Yahoo is seeing unusual traffic from your IP address and/or that emails from your mail server are generating complaints from Yahoo Mail users.

Our recommendations

  • The error is temporary. We encourage you to retry sending emails 4 hours after encountering the error.
  • If you're not the administrator of the mail server in question, we suggest you contact the administrator directly to discuss the error.
  • If you're an administrator of message content and 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 recommended guidelines for bulk mail senders and postmasters and note we don't disclose further information about our filtering practices.