Messages are exposed in the "announcement" query schema, making this data available for all standard query operations (grid views, export, API access, etc.). For example, you can view the query version of this forum, ordered from most recent message, via this URL:

https://www.labkey.org/query/home/Developer/Forum/executeQuery.view?schemaName=announcement&query.queryName=Announcement&query.sort=-Created

By applying the folder filter "Current folder and subfolders" the grid will include messages from all subfolders where the user has read permissions. You can also query subfolders programmatically using the containerFilter config option on selectRows().

You probably want to activate the "Messages" module in the folders where you perform these queries, otherwise the schema will be hidden.

Adam