Convert Public Folder Calendar to Shared Mailbox Calendar
Public Folder to Shared Mailbox Conversion:
1. Create shared mailbox
2. Backup the public folder in a .pst for safety
3. Copy all events from public folder calendar to shared mailbox calendar (Easiest if you do view -> list, and then CTRL A and drag and drop into the new calendar)
4. Review permissions on public folder then delete the public folder
5. Setup permissions on new shared mailbox (Users I don't think need to be members of the shared mailbox, only the admin accounts, admin accounts will open the shared mailbox and navigate to the calendar and edit the calendar permissions there)
6. Users will get email to automatically add the new calendar
7. Users need to delete the old calendar to avoid confusion
8. Optional - Set limit sizes on receive to 0KB to prevent emails being sent the the mailbox. Keep send on however or else invites in theory could break.