Follow these steps to set up calendar sync in Outlook 2013:
Create a connection to access the calendar in WebMail.
Download Latest CalDAV Add-on Archive for Outlook:

Unpack the zip archive.
Close the Outlook app.
Run the file CalDavSynchronizer.Setup.msi
and install it.
Start Outlook and in the "
CalDav Synchronizer»Click«
Synchronization Profiles»:

In the window that appears, select "
Generic CalDAV/CardDAV" and press "
OK»:

Enter the required information in the following fields:

Click "OK»And check if synchronization works.