When you have an existing UTmail+ account set up and are encountering issues, you can delete the existing account before adding it back to troubleshoot. The error may have arisen because the original account used legacy authentication, which requires you to delete the account and re-add the account while utilizing modern authentication. 

Note: Please back up your locally stored email messages from your email account before proceeding.

 

Consult these following knowledge articles for instructions on deleting an existing email account:

Desktop

Outlook 

UTmail+: Remove an existing email account from Outlook on Windows

UTmail+: Remove an existing email account from Outlook on Mac

Other email clients

UTmail+: Remove an existing email account from Windows Mail

UTmail+: Remove an existing email account from Apple Mail

UTmail+: Remove an existing email account from Thunderbird

 

Mobile

Outlook

UTmail+: Remove an existing email account from Outlook on Android

UTmail+: Remove an existing email account from Outlook on iOS mobile

Other email clients

UTmail+: Remove an existing email account from Apple Mail on iOS

UTmail+: Remove an existing email account from Android's Gmail app