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Error: "421 Message from (x.x.x.x) temporarily deferred - 4.16.50" when sending email to Yahoo

If you're the postmaster for a third party site that's seeing this error, here's some info to help move you forward.

"421 Message from x.x.x.x temporarily deferred - 4.16.50"

If this error is in your SMTP logs (where x.x.x.x is your IP address)

  • It indicates that emails from your mail server have been generating substantial complaints from Yahoo Mail users.
  • It's a temporary error and your mail server may automatically retry sending emails at a later time.
  • The IP (or its subnet, i.e., .255 ) is deferred due to being a poor sending reputation and low connectivity on our MTAs.

Are you the administrator for the message content or mailing policies?

After any compromised event, your sending reputation will take time to recover. It’s important to insure that you’re doing everything possible to improve your domain’s DNS/SMTP reputation within the industry. There are online resources available that allow mailers to check their current status on IP reputation lists.

  Good to know: Yahoo is unable to disclose specific information regarding our filtering practices.

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