That guide shows you how to install Zimbra without telling how to uninstall it.
Zimbra installed with a .sh file through Terminal is not shown in Ubuntu Software Center.
After some research, I managed to uninstall it with two simple steps below:
In Terminal cd to the folder:
--> :~$ cd ~/zimbra/zdesktop
Then enter
--> :~$ ./uninstall
Between Evolution and Thunderbird, I personally prefer Thunderbird which I'm more familiar with while Evolution sometimes is not responding when retrieving my gmails.