Kolab brings the ability to share data between different clients. It makes possible for your secretary to use Outlook and you use Kontact, for instance.

You will have a configuration interface which does user management, mail account setup, a central LDAP config data and addressbook server, spam and virus filtering, vacation scripts, free busy list handling, resource handling (rooms, cars), groups, distribution lists, automatic invitation handling, etc.

But that can cause initial setup troubles. For a newbie like me it means: a long long frustrating nightmare, and too much complexity to manage once working. So no, thanks, I'll go to simple IMAP.