How to see all the mailboxes a user has access to in CoreView

1. Under “Reports”, select “Security”, and then choose “User mailbox security”.

2. Here, apply a filter to the “Users with access” column using the user principal name of the user for whom you want to view all mailbox access. 
3. This will display all the mailboxes to which the selected user has access rights:
   1. The “Full name”, “User principal name”, and “Primary SMTP address” columns provide details about the mailboxes the user has access to. 
   2. The “Access rights” column indicates the level of access the user has to each respective mailbox.

From the user card

Alternatively, you can access this information from the user's “user card”. 

1. Search for the user using the search bar located in the top menu.
2. Under “Mailbox”, click on “See details”.

3. A wizard will appear. Under the “Permissions to other mailboxes" tab, you will see all the mailboxes to which the selected user has access rights.