Trying to integrate Zimbra calendars in Lightning, I ran into a couple of problems. So far I’ve found four different ways to do it in the internet:

1. ICS: http://zimbrahost.example.com/home/USERNAME/CALENDARNAME
2. ICS: webcal://zimbrahost.example.com/home/USERNAME/CALENDARNAME
3. ICS: webcal://<USERNAME>:<PASSWORD>@zimbrahost.example.com/home/USERNAME/CALENDARNAME
4. CalDAV: http://zimbrahost.example.com/dav/USERNAME/CALENDARNAME

Now the ICS solutions don’t work properly for me, the calendar entries are loaded but Lightning is unable to write to the calendar (when editing entries, deleting entries, creating new entries).

CalDAV is working, but only when using one calendar, as it seems. I created a second calendar in the Zimbra Webinterface though, and when I try to add the second calendar the CalDAV way, I get a yellow warning sign next to the calendar name saying “The calendar <name> is not available at the moment”. So CalDAV seems to be limited to one Calendar per user or server.

I didn’t find a solution yet.