The information here does not apply to single-machine installations.
Suppose you have several MailCOPA clients running, all accessing the same message store (database), and these clients are all logged in as the same MailCOPA user. When things are changed on one client, a notification is sent to all other clients so they can update their displays.
This is useful for instance if you have several personnel logged in as the same user, dealing with customer enquiries. If one person marks a message as seen, or deletes it, or moves it to another folder, this will immediately update on the other clients.
Similarly, if the list in the Mail Received window is deleted and/or refreshed, this window on the other clients will reflect the change.
Notifications are sent via port 7493 UDP, so this must be open on each client for incoming traffic - normally MailCOPA will amend the Windows Firewall on installation, but you may need to do this manually on third-party firewalls.
NOTE too that notifications will only work within the same subnet. This would apply for instance if you are accessing the database from outside your local network, most likely using a MySQL database.
Changing folder will always update the display, and you can force this too, using the F5 key.