Kindly follow the below steps to sync the webmail calendar with the outlook email client in ‘read-only’ mode

Step 1: Login to your webmail and go to the “calendar” tab.
Step 2: Then right click on the calendar that you would like to open and then select “edit”
Step 3: In the window that appears, enable the “private URL” and then copy that URL.
Step 4: Open you Outlook and go to the calendar section.
Step 5: Click on the “open calendar” tile and select “from internet” from the drop down menu
Step 6: Now, paste the URL (webmail private URL) in the field and then click “OK” to have the calendar open in Outlook.