Finding Inactive Mailboxes Based on Message Trace Data

This article covers how to use Exchange Online message trace data to find inactive mailboxes based on their message send activity. The script processes user mailboxes but can easily be adapted to process shared mailboxes too. This is only one way to find inactive maiboxes. The other methods mentioned in the article might be better suited to your purpose.

https://office365itpros.com/2024/11/29/find-inactive-mailboxes-tracing/