Add Holidays to Zimbra Calendar

https://www.zimbra.org/extend/items/view/holiday-calendar

Rename the downloaded archive to match the included XML file (first part of file name).

Select Flush zimlet cache if updating a Zimlet.

Zimbra Admin → Configure → Zimlets → Gear Icon → Deploy

If you don't see the Holiday Calendars zimlet, refresh your browser page.

Zimbra Web Client → Zimlets (scroll down on left) → Holiday Calendars → Subscribe (US Holidays)

Zimbra Web Client → Calendar → Select the checkbox to display the holiday calendar