17 535 5.7 3 Authentication Unsuccessful SMTP Office365.com Solutions

When trying to send emails via SMTP through Office365.com, you may encounter an "Authentication Unsuccessful" error. This issue can be frustrating, especially when you're trying to set up an automated email system or integrate with a third-party service. In this article, we'll explore five potential solutions to help you resolve this problem.

1. Double-Check Your Credentials

The first and foremost step is to ensure that you're using the correct credentials. This includes your Office365 email address and password. It's not uncommon to mistake a character or two, so carefully retype both and try again. If you've recently changed your password, make sure you're using the updated one.

2. Enable Less Secure Apps

Sometimes, Office365 blocks less secure apps by default for security reasons. You may need to log into your Office365 account and navigate to the security settings to allow less secure apps. This can be found under "My Account" > "Security & Privacy" > "Additional security verification." From there, you should see an option to allow less secure apps.

3. Use the Correct SMTP Settings

It's essential to use the correct SMTP server settings when configuring your email client or service. For Office365, the typical SMTP settings are:

• SMTP Server: smtp.office365.com
• Port: 587 (TLS) or 25 (no encryption)
• Encryption Method: TLS or None (depending on the port)

Make sure these settings match what's required by Office365 and are correctly entered into your email client or service.

4. Check Your Firewall and Antivirus Settings

Sometimes, firewall or antivirus software can block SMTP connections. Temporarily disable any such software and try sending an email again. If it works, you'll need to adjust your firewall or antivirus settings to allow SMTP connections.

5. Contact Office365 Support

If none of the above solutions work, it's time to reach out to Office365 support. There may be an issue with your account or a broader problem that needs to be addressed by Microsoft. Their support team can help diagnose and resolve the issue.

In conclusion, the "Authentication Unsuccessful" error when using SMTP with Office365.com can be caused by various factors. By following the steps outlined in this article, you should be able to narrow down and resolve the problem. Remember to always keep your credentials secure and use the correct SMTP settings to avoid any potential issues.

【AOTsend Email API】：AOTsend is a Managed Email Service for sending transactional emails. Support Email Types: reminders, authentication, confirmations, notifications, verification codes, invoices, password resets, account activations, billing statements, two-factor authentication (2FA), and one-time passwords (OTP) emails, etc. $0.28 per 1000 Emails. 99% Delivery, 98% Inbox Rate.

You might be interested in:
Why did we start the AOTsend project, Brand Story?
What is a Managed Email API, How it Works?
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?