A report that shows how many Active Directory accounts that have mailbox quota's set.
1. In MessageStats reports go to Mailboxes | Sizes And Quotas and click on the Mailbox Quotas report
2. If you are looking for everyone, it has a default of 10 mailboxes change that to the number of Mailboxes you have in your Exchange Org and click Apply Filters.
3. Anyone one that has the No Checking under the Storage Limit column does not have a Quota set everyone else has a Mailbox quota.
