Yahoo 421 errors are temporary rejections indicating problems with Yahoo's mail servers, potentially due to server load, maintenance, infrastructure issues, poor reputation, incorrect authentication, or exceeding sending limits. Resolving them involves retrying emails, contacting Yahoo's postmaster, reviewing your sending infrastructure, ensuring valid SPF records and rDNS, improving IP and domain reputation, warming up IPs, checking authentication methods (SPF, DKIM, DMARC), adhering to Yahoo's guidelines, managing sending volumes, and monitoring complaint rates.
8 marketer opinions
Yahoo 421 errors indicate temporary issues with Yahoo's mail servers, potentially due to server load, maintenance, or sender reputation problems. Resolution involves verifying sending infrastructure, ensuring valid SPF records, checking IP reputation, warming up IPs, checking authentication methods (SPF, DKIM, DMARC), adhering to Yahoo's sending guidelines, and reducing sending volumes.
Marketer view
Email marketer from Email Marketing Forum recommends reducing sending volumes to Yahoo addresses, especially if the error is persistent. This can help avoid being flagged as a potential spammer.
6 May 2023 - Email Marketing Forum
Marketer view
Email Marketer from Reddit suggests that a 421 error means your IP reputation could be suffering. He recommends checking blacklists and ensuring your sending practices are up to par with Yahoo's guidelines to repair your IP's reputation.
18 Dec 2024 - Reddit
4 expert opinions
Yahoo 421 errors are temporary rejections that can occur due to various reasons. Retrying the message is acceptable, but the issue may persist if the initial reason isn't resolved. Contacting Yahoo's postmaster can help address filter-related problems. Reverse DNS (rDNS) issues can also cause these errors, so ensuring a valid rDNS record is crucial. High complaint rates may lead to temporary blocks, highlighting the importance of monitoring feedback loops and addressing complaints promptly.
Expert view
Expert from Word to the Wise shares that high complaint rates may trigger temporary blocks resulting in 421 errors. Monitor feedback loops and promptly address complaints to maintain a healthy sender reputation.
3 May 2025 - Word to the Wise
Expert view
Expert from Email Geeks shares that you can contact the Yahoo team via their postmaster website to address filter issues. They may reset the filters and allow you to rebuild your reputation.
20 Jan 2024 - Email Geeks
3 technical articles
Yahoo 421 errors are temporary SMTP errors that indicate issues with the recipient mail server. The causes are related to server load, maintenance, or insufficient resources. The best course of action is to retry sending the email after a delay, treating the error as a soft bounce and queueing the message for later delivery.
Technical article
Documentation from SparkPost highlights that 421 errors are soft bounces and you should queue the messages for later delivery.
5 Apr 2025 - SparkPost
Technical article
Documentation from SocketLabs states that 421 errors generally indicate a temporary server issue. Possible causes include the recipient server being too busy, having insufficient resources, or undergoing maintenance. It's generally recommended to retry sending after a delay.
12 Aug 2022 - SocketLabs