Sorry if this is already a feature (I'm a Mattermost noob) but I haven't found a way of doing this yet...

If we are going to implement this, we WILL need a way to search all content (Public/Private channels, Direct messages and Archived) for legal queries!

This is a basic requirement of all software we implement within Government!

Note: I am currently using the Team edition as a trial, so maybe it is a feature in the Enterprise version??