Zimbra is open source and is easy to use. It is available in both as an on-premises system and a hosted solution by the various hosting providers. Although most of the features are similar to what one gets with one or more of the other email platforms, it is compatible to all the operating systems like Unix, Linux, Windows and Mac. It also depends on individual business requirements. Zimbra hosting
plans are also most cost-effective than the others. It also offers better integration with third party applications.