I am a network, systems, network services administrator and designer.
I create systems: authentication & authorization, backup, cluster, virtualization, replication, storage.
I implement groupware solutions eg email server with antivirus, antispam and external database authentication.
I am linking with each other different systems eg Windows and Linux; I finds and fixes errors in existing systems and networks; I create webapplication based on PHP and Javascript (extjs, jquery); I create and implement firewalls and them rules, VPN access and configuration; In large environments I'm using terminal systems based on Linux system.
For no small and multidomain environments I recommend Kolab groupware service with email, antivirus, shared resources, calendars, emails book and webmail application. The Kolab based on free software and has simple managment.