Please note that if you are not the administrator of the mail server in question, kindly contact your email administrator directly with the error message you are receiving.

If you are seeing an error code in your SMTP logs indicating that the messages you are trying to send are "temporarily deferred," this means that we have observed unusual traffic patterns from your IP address.

Below is a list of common SMTP error codes for you to review. If you do not see your specific error code in the list below, please search for the error code in the above help search box.

• 421 Message from (x.x.x.x) temporarily deferred - 4.16.50
• 421 4.16.55 [TS01] Messages from x.x.x.x temporarily deferred due to excessive user complaints 
• 421 4.16.56 [TS02] Messages from x.x.x.x temporarily deferred due to excessive user complaints 
• 421 4.7.1 [TS03] All messages from x.x.x.x permanently deferred
• 451 Resources temporarily not available - Please try again later [#4.16.5]
• 550 5.7.1 [BLXX] Connections not accepted from IP addresses on Spamhaus
• 554 5.7.5 (AU01) Message not accepted for policy reasons
• 554 Message type not allowed
• "4xx" or "5xx" error message

Please note that these typically are not permanent errors; your system may automatically retry after a while. We encourage you to try re-sending to our emails approximately 4 hours after you encounter this error. If, however, you are seeing this same error consistently over a 48-hour period, we encourage you to review our recommended best practices when sending to Yahoo! Mail.