I am the systems administrator of our company and we run a Kerio Connect mail server and use Outlook as e-mail client. From what I understand, Microsoft has made it much harder to make a decent connector since Outlook 2010 which is why Kerio’s offline Outlook connector is not very efficient. The Kerio Connect Client is their alternative for Outlook but it is just a browser that uses webmail with notification and system tray support and is not very useful. Both consume an obscene amount of memory.
eM Client is very similar to Outlook so I think our users can adapt quickly. eM Client also has a chat feature that could be used with Kerio Connect. I think if you could work together, eM Client could become a very good supported client for Kerio Connect. Since Kerio is also a Czech company, maybe you could just call them… (+420 377 338 901).
I also posted a similar message on their forum, just the other way around.