Error: "421 4.7.0 [TS02] Messages from x.x.x.x temporarily deferred - 4.16.56.1"

If you're receiving the error message "421 4.7.0 [TS02] Messages from x.x.x.x temporarily deferred - 4.16.56.1" delivery failure error (where x.x.x.x is your IP address) when sending email to Yahoo from a non-Yahoo Mail address.

This indicates Yahoo is seeing unusual traffic from your IP address. This traffic can result from things outside of the sender's control.

  • If you’re using a shared IP address - Mail traffic from other domains could be negatively affecting your IP sending reputation.
  • Use a dedicated IP address for your mail - contact your host provider to request using dedicated IP addresses to send your mail.
  • Keep an eye on your sender reputation - Even if you have a good reputation, users can vote your email as spam and affect your overall reputation.
  • We review IPs submitted for delivery issues and, based on our review, we may modify your reputation in our systems if needed.

Review our guide to industry standards and best practices and consider the following when you're sending email to Yahoo Mail addresses:

  • IP address reputation
  • URL reputation
  • Domain reputation
  • Sender reputation
  • DomainKeys Identified Mail (DKIM) signatures
  • (DMARC) authentication