Importing CSV files
Is there a way to import CSV files into Zimbra's calendar and contacts without using the Import Wizard or Outlook?
For your address book go to: Zimbra webmail > Options > Address Book (note .csv import/export options) – Calendar and Contacts Migration
Do the same for calendar entries.
You could also consider scripting something to use the REST interface:
https://wiki.zimbra.com/wiki/Calendar_and_Contacts_Migration#Migrating_via_REST