I was asked the following question recently: What are the minimum permissions necessary I need to grant a user in order for that user to be able to access the data in another user’s mailbox?
...
Updated Jul 01, 2019
Version 2.0
Blog Post
Manju,
To grant another user access to a second user's calendar you can either grant MAPI permissions on the second user's calendar or grant permissions on that user object in the Active Directory.
If you want to just share the calendar you will grant access from Outlook client. Here is the article with the steps:
290824 How to open another user's calendar or another folder in Outlook 2002
http://support.microsoft.com/default.aspx?scid=kb;EN-US;290824
If you want to grant permissions to access the calendar from the Active Directory side you will grant permissions on the second user's user object under "mailbox rights" (steps listed above).
The user being granted the permissions at the Active Directory level will need the full mailbox access and with that right the user will be able to access all folders in the second user's mailbox, not just the calendar. There is no way to specify the specific
mailbox items the permissions are applied to at this level.
Hope this answers your question!