Zimbra Desktop Zimbra Desktop is a free and open source email client application that gives you online and offline access to all your email accounts in one place. It’s cross-platform, available on Windows, Mac OS and Linux. Zimbra Desktop works with many types of email systems to synchronize email, contacts and calendar data between user’s mailboxes in the cloud and local data stored on your computer disk. While synchronization requires network connectivity, Zimbra Desktop can be used offline when the user’s computer is not connected to the network.