The popup is not an option in this case.

>
>If your users will have an application running under your control, you can use some kind of popup mechanism. If you need the alert to be real time (guess not if you considered email) you may use winsock. Otherwise, a check to a table/inbox would do it.
>

Windows Messenger is not an option. We cannot require that customers install it. Net Send is one solution we are looking at.

>If the users won't have some specific app running or not something under your control, you should rely on som OS service, like a NetSend or Windows Messenger (but thay have to have it set up, also).