GOT IT !
1. log-in as secretary
2. click on Calendar tag
3. right-click on Calendars label
4. click on Link to shared calendar
5. insert data (eg: email:
boss@zimbra.mydomain.com - path: Calendar)
6. done
Then it's just a matter of selecting the right calendar when creating an appointment.
FYI, I created an appointment on a wrong calendar (mine, instead of a shared one) and when I tried to edit it and change the calendar, I had an error.
Thanks a lot again,
MaRu