The server software will only run in Linux (and Solaris). You can access it from Windows, with whatever email client you want to use, like Outlook, Thunderbird, etc. It also comes with its own web-based client, which can be accessed from Windows, UNIX, Linux, Mac, etc.
If your concern is pushing data to a phone, that can be done from Outlook in Windows, or Zimbra also supports over-the-air syncing just like Exchange does. Over-the-air doesn't require a computer for the client, but you still have to run the server in Linux.
Server: Linux
Client: Windows, Linux, etc. |