I recently installed Zimbra in my office. Zimbra is actually a mail server that includes many other utilities like calender etc. The benefit of using Zimbra is that you don’t have to install whole bunch of tools separately like the mta, mda, the front end pages etc. So you only have to install Zimbra and sit back n relax checking your mails. Its configuration is simple enough for a layman to install it but its con is that if you install it with a wrong option, it’ll just crash your head :D.