Firstly, before I go through the test process myself: Can a calendar be shared to a group as described above. (I don't like the word "believe").
If so, I don't want users to be given any option in whether or not they accept the share. I just want the share to appear for them.
Imagine this scenario:
Catbert, Evil HR Director:"I want everybody to record their holiday leave requests on our new Company Calendar"
3 days later:
Catbert: "Where is Salesman John Doe today"
Pointy Haired Boss: "On Holiday"
Catbert:"Why has this not been recorded in the calendar ?"
Pointy Haired Boss: "What Calendar ?"
Catbert:"Remember, the one I told you about 3 days ago"
Pointy Haired Boss: "We could not see any calendar in our Zimbra Interface. Let me speak to Dilbert in IT and find out why this has happened."
An hour later:
Pointy Haired Boss: "Dilbert, why can't I see the company calendar in my Zimbra Interface"
Dilbert: "You were supposed to accept the request to join the calendar that appeared in your inbox"
Pointy Haired Boss: "Oh, I saw that email. It looked a bit technical and I thought it had been sent to me by mistake - so I deleted it"
Dilbert: "You're fired for being technically incompetent"
Pointy Haired Boss: "You're fired for insubordination"
See what I mean ?
Schrödinger's Birthday Present Experiment proves that:
"The contents of a box are much more interesting before the box is opened"