How can I resolve Yahoo SMTP error 421 4.7.0 TSS04?

Email marketer from MailerQ suggests ensuring the sending server's reverse DNS is correctly configured and matches the hostname. They also highlight the importance of list hygiene to avoid high bounce rates that can trigger temporary deferrals.

Email marketer from Email Geeks explains that the link in the error message leads to a section titled `Message temporarily deferred (eg: TS* Errors)` with information and potential next steps.

Email marketer from Litmus advises that if you are receiving TSS04 errors from Yahoo, you should carefully monitor your engagement metrics, specifically complaint rates. High complaint rates directly impact deliverability.

Email marketer from DNS Records details that if you send marketing emails, you should set the “rua” tag of your DMARC record to an email address dedicated to receiving aggregate reports. They advise ensuring your SPF record contains all IPs able to send emails on behalf of your domain.

Email marketer from Email On Acid recommends that if you are sending from a new IP address, you should “warm up” your IP address by gradually increasing sending volume. This helps establish a positive sending reputation with Yahoo.

Email marketer from Gmass explains that Yahoo and AOL require authentication, including SPF, DKIM, and DMARC. They also require a one-click unsubscribe in the header of messages, and advise senders to have DMARC set to quarantine or reject.

Email marketer from Stack Overflow suggests checking the sending IP's reputation against blocklists and ensuring proper authentication (SPF, DKIM, DMARC) are in place to resolve Yahoo TSS04 errors.

Email marketer from Email Sender recommends checking if you have recently increased your email sending volume significantly, as this can trigger temporary deferrals from Yahoo. Gradually increasing sending volume can help avoid this.

Email marketer from Reddit suggests monitoring your sending reputation using tools like Google Postmaster Tools and Sender Score to identify potential issues that may lead to TSS04 errors.

Email marketer from Email Geeks shares a Kickbox blog post to help further investigate email delivery problems at Yahoo: <https://blog.kickbox.com/how-to-fix-email-delivery-problems-at-yahoo/>.

Email marketer from SendGrid responds that to avoid delivery issues, you should implement a DMARC policy of `p=quarantine` or `p=reject` which instructs receiving mail servers on how to handle emails that fail authentication checks.

Expert from Email Geeks points out that the answer to the Yahoo error code is in the Yahoo Senders Best Practices documentation: <https://senders.yahooinc.com/best-practices>.

Expert from Word to the Wise suggests that maintaining a clean and engaged email list is crucial for avoiding delivery issues with Yahoo. Regularly remove inactive subscribers and focus on acquiring new subscribers through opt-in methods to ensure higher deliverability rates.

Expert from Email Geeks suggests searching the Slack group for the error message [TSS04] to find existing conversations explaining the issue.

Expert from Spam Resource explains that Yahoo's 421 errors indicate a problem with your email practices, such as poor list hygiene or low engagement. Focus on improving your sender reputation by removing unengaged subscribers and sending relevant content.

Expert from Word to the Wise emphasizes the importance of actively monitoring your sender reputation with Yahoo. Use Yahoo's feedback loop (if available) and monitor complaint rates to identify and address any issues that may be causing the TSS04 error.

Documentation from RFC Editor defines the 421 SMTP reply code as "Service not available, closing transmission channel." It indicates a temporary condition and the client should retry later.

Documentation from SparkPost advises checking your sending reputation if you encounter TSS04 errors. High complaint rates or being listed on blocklists may trigger this error. Rectifying reputation issues is key.

Documentation from Yahoo Help explains that a 421 4.7.0 [TSS04] error means messages are temporarily deferred due to unexpected volume or user complaints. They advise reviewing their best practices documentation and using their support channels if needed.

Documentation from Google Workspace Admin Help clarifies that 421 errors are temporary issues. They advise waiting and retrying sending the email later, as the issue might resolve itself.