How to know default webmail client that user uses for email box Horde or Roundcube on a cPanel server
To check the default webmail client that a user uses for their email box on a cPanel server, you can use the following command:
egrep "roundcube|horde" /home/*/.cpanel/nvdata/*_default_webmail_app
It will show a user, email box and default webmail app that set up by the user by default