If you are using a cPanel based VPS hosting or dedicated server you can activate or deactivate specific webmail clients you like. Just login to your cPanel's admin control panel and browse for "Tweak Settings" section in WHM (Web Host Manager).
To login to WHM adin area of your cPanel VPS or dedicated server use this web address in the web browser:
http://126.96.36.199/whm (188.8.131.52 is the main IP address of your cPanel VPS hosting server or dedicated server). You will be asked for username which is "root" account login and the root password for the server. You can also use an address in the browser in format: http://184.108.40.206:2086
Once you open the cPanel's admin area (WHM) Tweak Settings link, click on "Mail" tab. Then you will be able to select or deselect the webmail clients available for your VPS hosting server or dedicated server such as Horde, Squirrelmail, Roundcube. Select them to be active or inactive by checking or unchecking the corresponding option box.