This article will show you how to find the CalDAV URL for your 123-reg Mailbox Calendar. The CalDAV URL is the location of your calendar's server. This is what a mail client looks for when you want to sync your calendar, however, some clients, such as Mozilla Thunderbird need you to enter it directly.
To find your CalDAV URL, follow the steps below.
Log in to your 123-reg Mailbox using the webmail service.
Click on the Calendar icon from the menu bar.
From the list of available calendars on the left hand side of the screen, use the downwards pointing arrow button to open a menu. From the menu, click on the Properties option.
From the Overview panel, you will see you CalDAV URL.