You have 1,000 user accounts that are each licensed for Microsoft 365. Each user account has a Microsoft Exchange Online mailbox.
Ten of the user accounts are configured as service accounts for applications. The applications send event notifications to the mailboxes of the service accounts by using SMTP. The developers of each application have delegated access to the mailbox of their respective application.
You need to ensure that all the event notifications sent by the applications are retained in the service account mailboxes so that new developers can review older notifications. The developers must be able to view only the notifications for their respective application. The solution must minimize licensing costs.
What should you do?