@Vasil Michev Thank you for the reply! I have suggested the eDiscovery reports to the client and they are checking that out.
If they are really wanting to use PowerShell, any suggestions on how to do that? I'm thinking maybe the New-ComplianceSearch or Search-Mailbox cmdlets, but maybe I'm off base (will both of these allow searching ALL mailboxes in the organization with the date range criteria and report necessary information - total # messages, total size, etc)? If there is a better option, I'd appreciate the suggestion! Thank you!