For Yahoo Email help
If you are seeing the error code "421 Message from x.x.x.x temporarily deferred" or "451 Message temporarily deferred" in your SMTP logs, this indicates that the message you attempted to send was not accepted at Yahoo!. It is not a permanent error; your system will automatically re-try later.
If you are seeing this same error consistently over an extended period of time, and you feel that your policies and practices comply with our guidelines (described below), we would encourage you to contact 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, if appropriate, 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.
