Mailbox Permissions may include Users and Groups, and sometimes even nested groups. And you were tasked to get a report listing all those recipients, it would be a very tedious process to manually look up each entries. This script can help generate the needed report based on a file with a list of mailboxes are input file, all mailboxes, or just a single mailbox.
https://www.lazyexchangeadmin.com/2018/08/recursive-mailbox-full-permission.html