If you’re seeing the error “421 Message from x.x.x.x temporarily deferred – 4.16.50″, in your SMTP logs (where x.x.x.x is your IP address), this indicates that emails from your mail server have been generating substantial complaints from Yahoo! Mail users.

This is a temporary error and your mail server may automatically re-try sending emails at a later time. However, if you’re seeing this error consistently over an extended period of time, we encourage you to provide us with detailed information so that we can help diagnose your problem.

For bulk mailers, please visit this page to review our best practice recommendations and request assistance.

If your mail server does not primarily send bulk mailings (e.g., you run a personal, corporate, educational, or ISP mail server), please fill out this form instead.

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

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