When a client logs in to Cerberus FTP Server, Active Directory users have the option to login with their Security Account Manager (SAM) account or their User Principal Name (UPN) account.
If the default virtual directory mapping mode is set to Global Home/%USER%, or there is a %USER% variable in a directory path or name, Cerberus will use the username to create the home directory, which can be different if the user logs in as "exampleuser" or "email@example.com". By using the username to create the home directory, two separate home directories can be created if the user logs in using both SAM and UPN account names.
Having two separate home directories for users is not ideal and can end up causing problems down the road. Because of this, Cerberus allows you to modify User Policy and correct the potential problem.
To keep from having two home directories created when users login using their SAM and UPN accounts, you will need to select "Use User Principal Name (UPN) for AD user name variables". This can be found in the User Manager - Policy section in the Cerberus FTP GUI. Once you have checked the box, click "Save" and changes will take effect immediately on all new users.
*Please note, you will have to go back to any users home directories that were created before making this change and manually rename them to the User Principal Name (UPN).