Hello.
If the user properties of the field name, name and full name are not in English, the Outlook can not connect to the server openchange.
If these fields are renamed into English - all OK.
example 1:
username=Petrov
Name=Ivan
Surname=Petrov
Display Name = Ivan Petrov
This working fine.
Example 2 (Russian language):
Username = Petrov
Name=Иван
Surname=Петров
Display Name = Иван Петров
This not working
Tested
Zentyal 3.5.2 and MS Outlook 2010, 2013
Sorry for my bad English