Questions about reminders on shared folders comes up every few months.
We have a shared calendar that our workgroup can add appointments to. We want the reminders to show up for all the people it's shared with, but they are only popping up on the computer of person that created the item. Can we have the reminders pop up on all the computers that are sharing?
No. Reminders only fire for calendars in the accounts (listed in Account Settings) in your profile. Reminders in shared mailbox won't fire, in part because it has the potential to create "reminder spam".
There two options available: Users copy the appointments that they want reminders for to their own calendar. They can either open the appointment and click the Copy to My Calendar button or drag and drop a copy to their calendar.
When you create the appointment on the shared calendar, Save the appointment using the save icon or Ctrl+S then click the Copy to My Calendar button to copy and close it.
The other option is to give the users full access permission to the mailbox and have them add it to their profile as a separate account. If they add the shared mailbox as an account, remove it as additional mailbox (if added) and the Exchange administrator will also need to set automapping to false.