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Yahoo bounce message: 421 Temporary deferred - 4.16.50

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. If you are the administrator for the message content or mailing policies, we ask that you review outgoing messages for potentially objectionable content or practices.

Please know that Yahoo! is unable to disclose specific information regarding our filtering practices; however, we do publish recommended guidelines at this page for review.

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

Stop all this jibber jabber, what does it mean?

The SMTP server you are using has been abused by someone to send spam to Yahoo users and is temporary blocked by Yahoo. This usually takes just a few hours or less, depending on the spam level that Yahoo has been receiving.

Did I do something wrong?

No, probably not, unless you have been sending spam yourself. At this moment, the problem resides on the SMTP server of your outgoing email provider.

How can I fix this?

At this point there is not much you can do, but wait for one or a few hours; the problem will be fixed automatically over time.