At the Zarafa forum this is a thread:
This is also exactly the problem we face with outlook clients 2007/2010 (and possible 2013)
We have Zarafa client: zarafaclient-en-7.2.6-52189
And Kopano Core: kopano-server-8.3.0~1042-2.1.x86_64
Anybody can tell me how to disable the notifications for shared calendars because we are going crazy here.