You have a Microsoft Exchange Server 2019 organization that contains 5,000 mailboxes.
You purchase a Microsoft 365 E5 subscription and create a hybrid deployment. You configure all MX records to point to Exchange Online.
You purchase 2,000 Microsoft 365 E5 licenses, and you migrate 2,000 mailboxes to Exchange Online.
You need to identify which additional licenses must be purchased. The solution must minimize costs.
Which licenses should you identify?