Mail Undeliverable

Question

I receive a mail undeliverable email about 10 times a day for the past couple of months and the error message that says the log to paste when you open a support issue: 5.7.139 Authentication unsuccessful, the user credentials were incorrect. [SYBPR01CA0209.ausprd01.prod.outlook.com 2025-03-19T01:03:43.717Z 08DD66468F86EB47]

Can anyone help me with this?

Thanks

Answer 1

Dear Robert_223

Good day!

Thank you for posting to Microsoft Community. We are glad to assist!

Based on your description, I understand you concern with error 5.7.139 Authentication unsuccessful, the user credentials were incorrect.

To troubleshoot your issue, could you kindly have a try to do following steps?

May I know whether you are an end user or global admin in your organization?

Modern Authentication: Microsoft has been phasing out basic authentication in favor of modern authentication methods like OAuth. If your email client or application does not support modern authentication, you might encounter this error

If you are an end user, please ask your admin to check below:

1. Disable the Azure Security Defaults by toggling the Enable Security Defaults to No:

Caution

Don't do this step unless you understand the risks that are involved.

- Sign in to the Azure portal as a Security administrator or Conditional Access administrator.
- Browse to **Microsoft Entra ID** > **Properties**.
- Select **Manage security defaults**.
- Set the **Enable security defaults** toggle to **No**.
- Select **Save**.

2. Exclude the user from a Conditional Access policy that blocks Legacy Authentication:
   • Sign in to the Azure portal as a Security administrator or Conditional Access administrator.
   • Browse to Microsoft Entra ID > Security > Conditional Access.
   • In the policy that blocks Legacy Authentication, exclude the mailbox being used under Users and Groups > Exclude.
   • Select Save.

If it is convenient, could you kindly share me the SMTP settings for your account in Outlook? Make sure that TLS 1.2 is enabled on Exchange Server.

I look forward to your response.

Please note that our initial response may not always resolve the issue immediately. However, with your help and more detailed information, we can work together to find a solution.

Thanks for your precious time and your understanding would be highly appreciated. Have a nice day!

Best regards,

Allen | Community Moderator

Answer 2

Thank you for the reply!

1. URL is outlook.office.com
2. See below

Also, SMTP has been turned on and didn't resolve the issue

Answer 3

Dear User,

Thanks for your post in Microsoft Community.

I understand that you are encountering an issue with emails not being delivered, and you are receiving an error message stating “5.7.139 Authentication failed, user credentials are incorrect.”

I am very eager to help you resolve this issue, but I need to request more information about your account so that I can analyze your problem.

1. I would like to confirm whether the email account you use to log in is for company/school use or personal use? If it is a company account, please log into the account in a browser and confirm whether the current URL is outlook.live.com or outlook.office.com.
2. Provide a complete screenshot of the error message (win+shift+s).

I look forward to your answer. Please note that the information requested above is necessary for further analysis and resolution of your situation.

Thank you very much for your patience and cooperation.

Thank you for taking the time. Have a nice day.

Best regards

Yolanda - MSFT | Microsoft Community Support Specialist