Notes

There's lots of ways to share a calendar between two or more users with Exchange. However with Office 365, there's only one correct way to share the calendar such that it instantly and automatically syncs with Outlook (desktop app) and phone clients. If you don't share the calendar this way, expect for it to be a big pain in the ass and to probably not work.

Additionally, this procedure is only intended to be used to share calendars between members of the same organization.

Procedure

1. Log in to the OWA of the account that hosts the calendar that is to be shared.
   
   
2. Click the Calendar tab in the bottom-left:
   
   
   
3. Right click on the calendar to be shared, and choose "Sharing prmissions":
   
   
   
   
4. In the pop-out pane that appears on the left-hand side of the screen, put the sharee's email in to the "Send a sharing invitation in email:" field. Once you select a user, you can also choose the permission they should have for the calendar. Select a permission level and choose "Share".
   
   
5. Log out of the calendar owner's OWA.
   
   
6. Log in to the OWA of the user you specified in step 4.
   
   
7. Open the sharing email that was sent in step 4 and accept the invitation. You must do this in OWA!
   
   
   1. If the user is has the desktop Outlook application, close and re-open it and the calendar will now be there (but will need to be checked off to display it).
      
      
   2. If the user has the Outlook application on their phone, close and re-open it and the calendar will be there as well.