I’ve got a client with Kerio Connect as their mail/contacts/calendars server. They were seeing an issue on some workstations where when the user created a calendar event in their Kerio calendar, there was no option to invite people to the event. For other people in the same office however, this worked as expected.

Even more strangely, all of these accounts were set up using the Kerio Account Assistant, but likely at different times over a number of different Kerio updates.

The solution appears to be to configure a CalDAV account manually, using the Advanced setting.

Go into System Preferences and delete the existing calendar account. Then re-add the account as a CalDAV and select the Advanced account type. Enter the following details:

Username: The user’s full e-mail address (e.g. [email protected])
Password: The user’s password
Server: Full hostname of the Kerio server (e.g. mail.automatica.com.au)
Path: /caldav/users/domainname/username (e.g. /caldav/users/automatica.com.au/kai)
Port: 443
SSL: ticked.