Exchange Reporter Plus allows you to:
Get information about all IMs between users.
View the users with the most IM sessions.
List details about your users' IM sessions with external users.
View the IM filters configured in your organization.
Go to the Skype for Business tab.
Click the Instant Messaging sub-category.
Choose any of the 4 IM reports displayed in the next screen.
This way, you can keep an eye on how IM is being used in your organization.