How to grant read permission to a mailbox
If you want to grant only read permissions to a user mailbox, you can’t do this with the command:
add-mailboxpermission -identity User1 -AccessRights ReadPermission -user User2
This will only contribute to the fact that User2 can view the permissions on the user mailbox of User1. By default Everyone has this permission.
To grant read access to user (or group) you must perform some actions in Outlook. Open Outlook, with the profile of the user mailbox which you want other users to have access to, and go to :
Tools -> Options -> Delegates
There you can add the users and/or groups which need access.




