To resolve this issue:
Contact Your Administrator:
If you are using a work or school account, reach out to your Microsoft/Office 365/Outlook administrator to enable SMTP authentication for your account.Enable SMTP Authentication Manually:
Log in to the Microsoft 365 Admin Center.
Navigate to Users > Active Users.
Select the user experiencing the issue, then click Mail.
Under Mail Settings, locate SMTP Authentication and ensure it is enabled.
For more information, visit official documentation.