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 is 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.

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

If you're not the administrator of the mail server in question, please contact the administrator directly with the error message you're receiving.

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

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