This article list know compatibility with other Outlook add-ins:
Kerio Connect (http://www.kerio.com/products/kerio-connect/server)
Running "Kerio Connect" together with CRM for Outlook have a known issue in that at random intervals HTML emails will not render properly and instead show the raw text version. Only in combination of the two add-in does this happen.
We have been in contact with the people in charge of Kerio Connect but they refuse to help with locating the core issue so until they change their mind we can not recommend or support running these two add-ins in combination :-(