One of the issues with assigning full mailbox access to users and support personnel is that things change over time. People change roles, move to other departments, or even leave the organization. Keeping track of all of this and removing full access permissions when required can be challenging in a fast-paced environment. This recipe will allow you to solve these issues using the Exchange Management Shell to find out exactly who has full access permissions to the mailboxes in your environment.
To find all of the users or groups who have been assigned full access rights to a mailbox, use the Get-MailboxPermission cmdlet:
Get-MailboxPermission -Identity administrator | Where-Object {$_.AccessRights -like "*FullAccess*"}
You can see here that we are limiting the results using a filter by piping the output to the Where-Object cmdlet. Only the users with the FullAccess access rights will be returned.