I noticed that Zimbra uses a separate ICS file to store tasks. Tasks stored in Calendar(s) are ignored by Zimbra.
Thus, you have to add a second calendar in Lightning:
Code:
https://<server>/home/<username>/Tasks
This is just a workaround because it is not comfortable to work in Lightning this way: you have to specify the according calendar for each appointment/task.
Does anyone see a solution to this?