Hi,@Jimhex2024
Thanks for posting your question in the Microsoft Q&A forum.
There's no native feature available in Exchange to track the change of read/unread status of a mail in the shared mailbox.
While the mailbox audit log will record user actions on it, it won't record actions such as marking items as read/unread at all.
You can refer to this link for details:https://learn.microsoft.com/en-us/purview/audit-mailboxes#mailbox-actions-for-user-mailboxes-and-shared-mailboxes
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