SMTP error code table

If you've received an SMTP error code when sending email to a Yahoo Mail account, here's information about the most commonly seen SMTP codes and their causes. For more details about each specific error code, review our 4xx SMTP and 5xx SMTP error code articles.

 Good to know - Yahoo is unable to disclose specific information regarding our filtering practices.

SMTP Error Diagnostic Error Message Reason
 421 421 Message temporarily deferred - [numeric code] The message content contained objectionable content, we're seeing unusual traffic from your servers, or emails from your mail server are generating complaints from Yahoo Mail users.
 421 421 4.7.0 [TS01] Messages from x.x.x.x temporarily deferred due to user complaints - 4.16.55 We're seeing unusual traffic patterns from your server. Submit your sending IPs for review.
 421 421 4.7.0 [TS02] Messages from x.x.x.x temporarily deferred due to user complaints - 4.16.55 We're seeing unusual traffic patterns from your server or your mailings are generating complaints from Yahoo Mail users. Submit your sending IPs for review.
 421 421 4.7.1 [TS03] Messages from x.x.x.x permanently deferred. Retrying will NOT succeed We're seeing a high volume of e-mails from your server that are indicative of unsolicited mailings. Submit your sending IPs for review.
 451 451 Resources temporarily not available - Please try again later [numeric code] This error indicates that our servers were busy and temporarily unable to process your transaction at the time of connection.
 451 451 VS1-IP Excessive unknown recipients - possible Open Relay (#4.1.8) Your mail server is configured as an open relay or proxy. Review our guidelines for avoiding deprioritization.
 451 451 VS1-MF Excessive unknown recipients - possible Open Relay (#4.4.5) The senders MAIL FROM address has been sending to excessive bouncing accounts (non-active, don't exist). Review your mailing lists, and remove any addresses that generate bounces.
 553 553 5.7.1 [BLXX] Connections not accepted from IP addresses on Spamhaus PBL The sending IP is listed on a Spamhaus blacklist. You can check your status on Spamhaus' site.
 554 554 Message not allowed - [numeric code] Your emails have become deprioritized due to the message content triggering our filters. We ask that you review the email's header and message content for potentially objectionable content. 
 554 Delivery error: dd This user doesn't have a yahoo.com account (******@yahoo.com) [-5] - mta1126.mail.gq1.yahoo.com [BODY] The Yahoo account that you're trying to send to doesn't exist. We recommend that you contact the recipient directly to confirm their correct email address.
 554 554 5.7.9 Message not accepted for policy reasons Your message wasn't delivered because Yahoo was unable to verify that it came from a legitimate email sender.