I am going to write a quick blog post on a procedure I am using to monitor inactive Exchange Distribution Groups.
Exchange Distributions Groups can grow out of control, especially if you have been running Exchange for a long time. One of the items I never see is a clean up process to remove inactive groups.
I discovered a powershell script someone else wrote that I modified and use to notify me of groups that have not been emailed in 90 days. It will write an a number to a custom attribute on the group object in Active Directory and reset it to zero if the group receives an email. Once it goes over that number, it will send you an email that the group has not been emailed in 90 days. This script will need to be scheduled on a scripting or utility box and will needs to be ran monthly.
I have found the script to be an effective way to remove unused groups. I will warn you of a law in this script, it does not seem to do a great job with nested email groups, so if you are being alerted to a nested group, you need to double check to ensure that the group is not in use.
You can download the script here.
I hope this helps others eliminate unused Exchange groups.