Hey @sylvain g​! Daniel from Customer Support Engineering here 🔧 

We currently don't have a native reporting tool that will display these statistics. The only way to achieve this would be by using our List all conversations endpoint. This will list all conversations on your workspace, which you could filter down by user ID to single out a particular user. To get every message per the user, you must retrieve a single conversation using the conversation's ID - the returned object will return "conversation parts", which are essentially messages that were sent by users and admins during the conversation. This should give you all of the users' messages and conversations!

I know it's not the cleanest way to do this as it requires a lot of API calls and data filtering - but this is the closest thing to a solution that I can offer at the moment.

Hope this helps! 🙌