19 Microsoft 365 Smtp Authentication Unsuccessful Solutions

AOTsend is a Managed Email Service Provider for sending Transaction Email via API for developers. 99% Delivery, 98% Inbox rate. $0.28 per 1000 emails. Start for free. Pay as you go. Check Top 10 Advantages of Managed Email API

When it comes to using Microsoft 365 for email communication, one of the most common issues users face is SMTP authentication failures. This can be frustrating, especially when you're trying to send an important email. In this blog post, we'll explore 19 solutions to help you troubleshoot and resolve SMTP authentication unsuccessful errors with Microsoft 365.

1. Check Your Credentials

First and foremost, ensure that you're using the correct username and password for your Microsoft 365 account. Often, authentication failures are caused by simple typos or mix-ups in credentials.

2. Update Your Password

If you've forgotten your password or suspect it may have been compromised, reset it immediately. A fresh password can sometimes resolve authentication issues.

3. Verify SMTP Settings

Double-check your SMTP server settings. For Microsoft 365, the typical SMTP server setting is smtp.office365.com, and the port is usually 587 or 25. Ensure these are correctly configured in your email client or application.

4. Enable Less Secure Apps

Microsoft 365, by default, might block less secure apps from accessing your account. You may need to enable less secure app access in your account settings.

5. Two-Step Verification

If you have two-step verification enabled on your account, you might need to generate an app-specific password for SMTP authentication.

6. Check Your Firewall Settings

Sometimes, firewalls can block SMTP connections. Ensure that your firewall allows outbound connections on the SMTP port you're using.

7. Update Your Email Client

If you're using an outdated email client, it might not support the latest authentication methods. Updating your client to the latest version could resolve the issue.

8. Review Your Account Status

Make sure your Microsoft 365 account is active and hasn't been suspended or disabled due to policy violations.

9. Clear Cached Credentials

Your email client or application might be using cached credentials. Clearing these and re-entering your credentials can help.

10. Disable Antivirus Scanning

Antivirus software can sometimes interfere with SMTP connections. Temporarily disable any antivirus scanning to see if it's causing the authentication issue.

11. Check TLS Settings

Ensure that your email client or application supports and is configured for TLS encryption, as Microsoft 365 requires this for secure connections.

12. Contact Your Administrator

If you're part of an organization, there might be additional security policies or firewall rules in place. Contact your IT administrator for assistance.

13. Review Microsoft 365 Service Health

Check the Microsoft 365 Service Health Dashboard to see if there are any known issues or outages that might be affecting SMTP authentication.

14. Use the Microsoft 365 Support and Recovery Assistant

Microsoft provides a Support and Recovery Assistant tool that can help diagnose and resolve common issues, including SMTP authentication problems.

15. Check for Third-Party App Conflicts

If you have installed any third-party apps that integrate with your email, they might be causing conflicts. Disable or uninstall these apps to see if they're the culprit.

16. Review Your DNS Settings

Ensure that your DNS settings are correctly configured for Microsoft 365. Incorrect DNS records can cause authentication issues.

17. Update Your Operating System

An outdated operating system might not support the latest security protocols. Keeping your OS up to date can help resolve compatibility issues.

18. Test with a Different Device or Network

Try authenticating from a different device or network to rule out any local issues that might be causing the problem.

19. Contact Microsoft Support

If none of the above solutions work, it's time to reach out to Microsoft Support for further assistance. They can help you troubleshoot and resolve the issue directly.

In conclusion, SMTP authentication failures with Microsoft 365 can be frustrating, but they are often solvable with a bit of troubleshooting. By following the solutions outlined in this blog post, you should be able to resolve most authentication issues and get back to sending emails without any hiccups.

AOTsend adopts the decoupled architecture on email service design. Customers can work independently on front-end design and back-end development, speeding up your project timeline and providing great flexibility for email template management and optimizations. Check Top 10 Advantages of Managed Email API. 99% Delivery, 98% Inbox rate. $0.28 per 1000 emails. Start for free. Pay as you go.

【AOTsend Email API】：
AOTsend is a Transactional Email Service API Provider specializing in Managed Email Service. 99% Delivery, 98% Inbox Rate. $0.28 per 1000 Emails.
AOT means Always On Time for email delivery.

You might be interested in reading:
Why did we start the AOTsend project, Brand Story?
What is a Managed Email API, Any Special?
Best 25+ Email Marketing Platforms (Authority,Keywords&Traffic Comparison)
Best 24+ Email Marketing Service (Price, Pros&Cons Comparison)
Email APIs vs SMTP: How they Works, Any Difference?