It occurs most often while trying to send an email message via the platform. Although the most common cause is improper SMTP configuration, there are many other factors that could cause this error. However, we’ll only focus on some of the most common ones, with emphasis on how to resolve the issue. Read about our solutions in detail below.

How can I fix Error 421 cannot connect to SMTP server in Outlook?

Conclusion

All things considered if you’re getting The server responded: 421 cannot connect to SMTP server error while using Outlook, there are a few ways you can fix it. Hence, checking the configuration is the first method we recommend in this guide. To reconfigure your SMTP settings in Microsoft Outlook, follow the steps outlined below: If the problem persists, we recommend you try our next fix. Note: The above-outlined steps can be used with Microsoft Outlook 2016 and above. To some extent, this may interfere with your browsing behavior, including your access and transmission of emails in Outlook. While VPNs have little or no direct influence on email transmission, VPN interference with Internet-based programs like Outlook is not uncommon. Hence, you can check if the error is caused due to interference from your VPN by simply disabling it for a moment. After disabling your VPN service, you can try to send an email; if the email goes through without an issue, the VPN is probably the cause of the error. In this case, we recommend you try a different VPN service.  The best VPNs for Windows 10 PCs are up-to-date and continuously optimized to be as error-free as possible. In rare cases, this could be the issue when The server responded: 421 cannot connect to SMTP server error occurs. You can check, to ascertain the culpability of a security program on your system, by disabling it, and then try sending an email. If the email goes through without a hitch, the security program (antivirus, firewall, antimalware) is obviously the cause of the error. To resolve this, you can reconfigure your AV or security program to grant permissions or exclude the email SMTP server from all advanced security checks and restrictions. If you have no idea how to go about this, you can easily disable the firewall or AV anytime you want to send an email and re-enable it shortly after. Our recommendation is to try all of our suggested fixes one by one and don’t skip either one of them. Check out our Outlook Hub to learn more about this Microsoft product. Visit our Outlook Troubleshooting section for more fixes and easy-to-follow guides. Have you successfully fixed the error? Which of our suggestions worked best for you? Tell us all about it in the comments section below.

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