\\[destination]\mailslot\\messngr is undocumented mailslot name, though it is widely used exactly for this purpose -- for sending popup messages. As I already mentioned, this is an equivalent of NET SEND command.
In this example a message is sent to the local computer, just to avoid disturbing others. As a destination, you also can choose any computer or server name on your LAN. An asterick (*) is for the primary domain. With this name chosen as a destination you will be granted an immediate attention of all your co-workers.
On target computer, TCP port 139 (NetBIOS) is assigned to receive messages.
Also the NetMessageBufferSend function (Unicode-based) can be used for sending messages on a network. If compared to this function, the mailslot approach can send messages no longer than 128 characters. Though it returns much faster than sometimes the NetMessageBufferSend does.
Credits: PHP (4.4.9), an HTML-embedded scripting language,
MySQL (5.1.55-log), the Open Source standard SQL database,
AceHTML Freeware
Version 4, freeware HTML Editor of choice. Hosted by Korax Online Inc.
Using mailslots to send messages on the network 
