What do Yahoo 421 errors mean and how to resolve them?
Summary
What email marketers say8Marketer opinions
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.
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.
Email Marketer from StackOverflow explains that ensuring you have setup valid SPF records can help resolve 421 errors as this could be a reason why the server thinks you aren't valid.
Email Marketer from MailerQ suggests that a 421 error from Yahoo can be a sign that there are issues with your sending infrastructure or setup and that you should review these before sending again.
Email marketer from Gmass describes that Yahoo uses throttling to protect their system and that these 421 errors could be due to too many connection attempts at the same time. You should throttle your sending to meet their guidelines.
Marketer from Email Geeks points out the importance of carefully reading Yahoo's best practices guide which is Yahoo's way of observing user reactions to email before adjusting sending throttle.
Email marketer from Litmus shares that you should check your authentication methods, in the form of SPF, DKIM and DMARC. Incorrect or missing DNS settings can cause deliverability issues with Yahoo.
Email marketer from EmailOnAcid notes that a common reason for 421 errors, particularly with new IPs, is the lack of a proper IP warmup. Ensure that you have warmed up your IP correctly by following guidelines. You will also want to ensure your domain reputation is high, this is also a factor.
What the experts say4Expert opinions
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.
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.
Expert from Spam Resource explains that an issue related to reverse DNS (rDNS) might cause 421 errors. Make sure your sending IP has a valid rDNS record pointing to your domain.
Expert from Email Geeks explains that 4xx errors are temporary rejections at the SMTP level, meaning retrying the same message is acceptable, but Yahoo may still reject the message if the initial reason for deferral persists.
What the documentation says3Technical articles
Documentation from SparkPost highlights that 421 errors are soft bounces and you should queue the messages for later delivery.
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.
Documentation from Yahoo Help Central explains that 421 errors are temporary SMTP errors indicating a temporary problem with the mail server. The cause may be load-related issues or maintenance. Retry sending the email later.