Welcome to our forum! Please kindly understand that the Outlook tag here we mainly focus on general issues about Outlook desktop client. For better research, please provide more information about this case:
What did you refer to in your previous question?
What is your account type (POP/IMAP/Exchange)?
What are you doing when you get this error?
Based on my search for error codes, here are links to several possible causes for this issue:
Error: Authentication unsuccessful.
Please also have a check if the security default is enabled in the tenant.
Hope this helps!
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