Kerio MailServer is what's known as a "groupware server" which basically means it allows several companies or organisations to collaborate on it at the same time.
Kerio MailServer does this through email, shared contacts, shared calendars and tasks. Kerio MailServer does this in complete security because it is integrated with McAfee Antivirus which enables it to instantly remove viruses from incoming and outgoing email. Likewise, SpamEliminator automatically detects and filters spam from the Kerio MailServer.
Kerio WebMail is particularly easy to use. You can drag and drop mails to an extent that's not possible in Outlook but at the same time, it can be used in conjunction with Outlook because Kerio MailServer Server-based calendars and address books synchronize seamlessly with both Outlook, Entourage and of course, Kerio WebMail. You can even migrate data and messages from Outlook on anything held on an MS Exchange server with a handy wizard.
If you're looking for a good alternative to Outlook with more drag-and-drop features and need group collaboration options, Kerio MailServer is worth a try.