There are multiple causes for the Kopano ribbon not being available in Outlook.
In heavily restricted environments you may get a startup exception with an error message along the lines of:
Access to the path "C:\Windows\Microsoft.NET\Framework\v4.0.30319\Config\machine.config" was denied.
While KOE does not use .net 4.0, but 4.5, this error will stop Outlook from further loading the plugin. You have to allow your users write access to the file to use KOE.
While starting up KOE checks if any Z-Push accounts are configured in your current profile. If no account has been configured, the ribbon will not be shown, even if the add-in is correctly loaded.
We've taken steps to reduce the chances of this happening release 1.3, by resolving KOE-87.