Well I don't know much about Kerio, but:
1) We're Open Source. They're not.
2) Hmmm, according to their forums, they have x users. We have x users. 1 Moderator, we have 8. Better forum support
3)
Kerio Technologies | Technical Support | Security Advisory
Kerio Key Features
Wireless email and groupware synchronization without middleware.
->Yup, Got that.
Integrated McAfee Antivirus instantly removes viruses from incoming and outgoing email.
->ClamAV (Which is Open Source too)
Multiple anti-spam technologies for the most effective spam control.
->[
AWL=0.042, BAYES_00=-2.599, HTML_50_60=0.134, HTML_FONT_LOW_CONTRAST=0.194, HTML_MESSAGE=0.001]
Kerio WebMail with drag-and-drop makes a great alternative to Microsoft Outlook.
->Hmmm, Sound familiar? Do they have a toaster? Cuz we do
Server-based calendars and address books synchronize seamlessly with Outlook, Entourage, WebMail, and mobile devices.
->Yup, that too.
Exchange Migration Tool imports all user data from Microsoft Exchange.
->Exchange, Lotus, Domino, PST Import tool
We're better.
