You can automate calendar backups by using the following Linux command and add it to a crontab on a server or machine to run on regular intervals:

your email address,
your email address password
The location where you want to save the resulting .ics file.
Can be found when you log into Zimbra. Select the calendar you want to download, and select Share Calendar. The URL will be given as a link at the bottom of the new window that opens. You want the one that mentions “ICS”.

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