Authentication in Outlook
In this problem, there may be two cases either the Outlook Express POP3 client is not able to access the mailbox because it does not exist or there is a custom recipient in the Exchange Server that has the same POP3 client as yours and Exchange Server is trying to access the custom recipient before accessing your mailbox.
How to Log in to the server by using Distributed Password
Open the Outlook Express
↣ Go to Tools menu
↣ Click Accounts
↣ Select any mail account using Log On option.
↣ Select the Clear Text option.
↣ If this works, then you were trying to access the wrong mailbox.
↣ If this does not work, then the administrator needs to remove the custom recipient.
Authentication in Outlook | How to Log in to the server by using Distributed Password