You would think there was an easy way to check Exchange Onine distribution list are being used or are stale/not required and can be removed but there is not.

Tony Redmond has come to the rescue again and provided a script to help identify unused distribution lists: https://office365itpros.com/2026/07/09/inactive-distribution-list-2026/

Hopefully at some point Microsoft can add some metadata to each list to automatically record this information and make it easier for admins.