SMTP server authentication Error

Anonymous
2025-04-04T11:47:44+00:00

please help to solve this error

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.57 Client not authenticated to send mail. Error: 535 5.7.139 Authentication unsuccessful, basic authentication is disabled. [PN2****CA0106.INDPRD01.PROD.OUTLOOK.COM 2025-04-04******]

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  1. Vincent Choy 11,250 Reputation points Volunteer Moderator
    2025-04-07T05:45:46+00:00

    better don't use Basic Authentication...

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  2. Anonymous
    2025-04-07T05:05:45+00:00
    1. Are you using an email client (e.g., Outlook), a script, or an application to send mail?

    Answer: I am using a script to send mail (via C# application).

    1. Are you using a username/password (Basic Auth) or OAuth 2.0?

    Answer: I am using username/password (Basic Authentication).

    1. If OAuth, have you registered an app in Azure AD?

    Answer: Not applicable, as I’m currently using Basic Authentication.

    1. Is this for a shared mailbox or a licensed user?

    Answer: This is for a licensed user account.

    1. Does the account have an Exchange Online license?

    Answer: Yes, the account has an Exchange Online license.

    1. Is SMTP AUTH enabled for the account?

    Answer: No, SMTP AUTH is disable for this account.I need to enable this.

    1. Did this work previously, or is it a new setup?

    Answer: This is a new setup.

    1. Has your organization recently enforced Security Defaults or MFA?

    Answer: No idea for this

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  3. Anonymous
    2025-04-04T14:18:45+00:00

    Dear EINNOSYS Technologies,

    Thank you for reaching out to the Microsoft Community. I understand you’re encountering the error "535 5.7.139 Authentication unsuccessful, basic authentication is disabled" when trying to send mail via SMTP. This typically occurs when:

    1. Basic Authentication is disabled (as noted in the error), which is the default for Exchange Online to improve security.
    2. SMTP AUTH isn’t enabled for the account in use.
    3. The client/application is not configured for Modern Authentication (OAuth 2.0).

    To help to investigate this, please provide the following details:

    1. Are you using an email client (e.g., Outlook), a script, or an application to send mail?
    2. Are you using a username/password (Basic Auth) or OAuth 2.0?
    3. If OAuth, have you registered an app in Azure AD?
    4. Is this for a shared mailbox or a licensed user?
    5. Does the account have an Exchange Online license?
    6. Is SMTP AUTH enabled for the account? Enable or disable SMTP AUTH in Exchange Online | Microsoft Learn
    7. Did this work previously, or is it a new setup?
    8. Has your organization recently enforced Security Defaults or MFA?

    Let me know the answers to the above, and I’ll guide you further!

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