If you happened to set the Autoload feature of your preferred webmail application to zero seconds and now it won’t let you change to a different webmail application, here is a very easy fix to disable webmail from autoloading, whether you chose Horde Webmail or Roundcube.
1. Log in webmail by using URLs:
https://www.YourDomain.com/webmail/ or https://www.YourDomain.com:2096
2. Once you are automatically redirected to your webmail, click on cPanel Webmail Home.
These are how the look like for:
Horde
Roundcube
3. Ensure that the Open my inbox when I log in box is unchecked.
4. You are done. The autoload feature has been disabled for your webmail.