I've seen some chatter on this but just for the sake of clarity I will ask...
Osticket can use the header "message-id" to match emails with existing tickets.
We see the behavior that when a ticket is closed and then someone replies to the original email thread (not the ticket thread) the ticket is re-opened but nobody receives an email notification. This may not even be unique to re-opened tickets, this may be just a function of new emails matched to to the ticket via message ID not generating message alerts but I have not dug in that deep.
Is there anyway to make this alert the agent that there's a new message?