sharing calendar for a group of users

[supportsib]

shared calendar
Hi,

I am trying to a create  shared calendar for  a group which contains more than 1000 users 

I created a shared mailbox  and I can see the calendar .

The problem is everyone can add and edit events 

Any other solutions 

Thanks

[#2]

See https://community.spiceworks.com/topic/1540519-read-only-permission-for-delegated-office-365-calenda...