If you have created one or more email account(s) through Plesk and you have enabled the webmail, you can change its issuing from Horde to Roundcube and vice versa. In order to make that change, take the following steps:
1. Log into myTophost Panel and then click on Plesk Login in order to connect to the Plesk of the plan that you are interested in.
2. In the Websites & Domains tab, click on Show More.
3. Click on Mail Settings.
4. Select the desired webmail from the drop down menu and click on Apply and ΟΚ.