One of the most popular webmail applications, Atmail, is now available for cPanel (versions 11.28+). If you have a dedicated server or VPS and would like to install it, the setup can be done fairly easily:
1) Log into WHM as root or a root-level reseller
2) In the left-hand column, click on Manage Plugins.
3) Check the “Install and keep updated” checkbox for the Atmail Open Source plugin.
4) Click the Save button at the bottom of the page.
If you need any assistance just let our Support staff know and we would be happy to help you out.
Source: http://www.cpanel.net/2011/05/atmail-we ... lable.html