How to resolve SMTP 421 errors with Web.de and GMX.net due to rate limiting?

Email marketer from SparkPost recommends checking your sending volume and reputation. If your volume is high and your reputation is low, you could hit rate limits. Additionally, they advise contacting the recipient's email provider for assistance.

Email marketer from StackOverflow recommends checking your mail server logs for more detailed error messages. Implement retry logic in your sending application to automatically resend emails after a delay. Contact the recipient's mail server administrator to inquire about their rate limits.

Email marketer from EmailToolTester advises segmenting email lists and personalizing messages. Sending targeted content to engaged subscribers increases open rates and click-through rates, which improves sender reputation and deliverability.

Email marketer from Email Geeks shares that they are getting SMTP status 421 temp fails from Web.de and GMX.net, pointing to rate limiting. They have reduced sending to 5 per minute, contacted them, and are considering stopping sending and re-warming up. They have since created a ticket with Mailgun and Web/GMX pointed to look into IPs

Email marketer from Mailjet suggests that rate limits are usually in place to prevent spam and abuse. They suggest monitoring your sending reputation, authenticating your emails and warming your IP address as the best practice.

Email marketer from GMX advises that if you are receiving 421 errors due to rate limiting, reduce the number of emails sent within a specific timeframe. If you continue to experience issues, contact their support team for assistance.

Email marketer from Web.de suggests ensuring your sending server has a valid PTR record. They also recommend following best practices for email authentication (SPF, DKIM, DMARC). If problems persist, their postmaster team should be contacted.

Email marketer from Reddit recommends gradually increasing sending volumes when warming up new IPs or domains. Start with low volumes and steadily increase over time, monitoring deliverability and engagement metrics.

Email marketer from Reddit suggests warming up IPs. Implement proper authentication (SPF, DKIM, DMARC). Ensure your sending domain has a clean reputation. Monitor bounce rates and feedback loops. Throttle sending volume, especially to new domains.

Email marketer from ServerFault suggests ensuring your server's IP address has a good reputation and is not blacklisted. Also, check your reverse DNS records and ensure they are properly configured. Try varying your sending patterns to avoid triggering rate limits.

Email marketer from Email Marketing Forum highlights the importance of maintaining a good IP reputation. They suggest using reputable sending platforms, monitoring blacklists, and actively managing sender reputation.

Expert from Word to the Wise explains the importance of maintaining a good sending reputation to prevent deliverability issues. Monitoring sender scores, promptly addressing complaints, and adhering to email best practices are crucial for building trust with ISPs.

Expert from Email Geeks explains that one of the German companies is particular about authentication aligning and technical aspects like rDNS. Stopping sending and slowly warming up the list is likely the fastest resolution. They are also SERIOUS about getting the technical bits right. They will also count their own retries when rate limiting. Furthermore, <http://web.de|web.de> and associated domains are picky and insist on DMARC style alignment for delivery.

Expert from Spamresource.com explains that throttling is a temporary delay in message delivery applied by the receiving server, often indicated by a 4xx SMTP response code. The sender should reduce sending volume and retry delivery later.

Documentation from Sendgrid provides an in-depth guide on email authentication standards such as SPF, DKIM, and DMARC. They emphasize the importance of implementing these measures to improve email deliverability and reduce the risk of being flagged as spam.

Documentation from RFC Editor states that a 421 SMTP error code indicates the service is not available and the connection will be closed. The server knows a condition that will improve if the command is repeated. The client is advised to try again later.

Documentation from Microsoft explains that Exchange Online implements rate limiting to protect the service. If you exceed these limits, you may receive temporary errors. They advise reviewing your sending patterns and ensuring compliance with their sending policies.

Documentation from IONOS explains that SMTP error 421 signifies a temporary server issue, suggesting the recipient server is unavailable. They recommend waiting and retrying later, as the server might be overloaded or undergoing maintenance.