When you mention a company or role in the comments under the activity section of "Submittals", only assignees would receive email notifications, but no one else from that same mentioned company or role would receive email notifications.
This is already working for "Issues" and "RFIs", so Autodesk should fix this with "Submittals" as well since the option to mention companies/roles in the "Submittals" activity is already there , but it only works with assignees.