I created a new calendar in Thunderbird that syncs to one of my iCloud calendars. I used the calDav method and changed the calendar link accordingly per some instructions I found online specific to setting up new calendars in calDav. My iCloud calendar link pre-fix: webcal://p08-calendarws.icloud.com/ca/subscribe/1/XXXXXXXXXXXX I changed it to (per calDav instructions): https://p08-caldav.icloud.com/ca/subscribe/1/XXXXXXXXXXXX I also followed Apple's new two-factor authentication process and app-specific password generation for Thunderbird. When creating my calendar, I used my normal iCloud username with that app-specific password. The calendar successfully creates in that I do not get any errors using that username/password combination. It's not rejected. The problem is that the calendar will not stay online. I can see it in my list of available calendars but the checkbox is unchecked and it will not let me check it. I've even done right-click > properties and tried to enable it that way and it briefly comes online and then disables again (less than 5 seconds). I'm using Linux CentOS 7 with the latest version of Thunderbird installed, which I know has the Lightning calendar plug-in now integrated. I should also mention that this exact process works just fine in Evolution using calDav. However, I really want to use Thunderbird because I've used it for years on Windows and Max OSX but if I can't get my calendars integrated, it will be a show-stopper for me. Does anyone have any idea why the network calendars will not stay enabled? Thanks!