OK, thanks.

What if, lets say, 5000 users have this program where they can only receive messages about weather, traffic, etc.

Now I would like to send a message to all these 5000 users (via MSN for instance) to inform them about new updates or something.

How can I do this??

Besides, the program does not have to be always running. The moment the program starts it justs downloads and displays all messages that were sent to it.
Maybe I could do this by adding a response check, that if the program doesn't react when a message is sent, the message is automatically saved on the server.

Please help.