I'm not sure what you are using the messaging for, but I want to repeat a couple of my earlier points because if they are important to you they mean that you should *not* be looking for a net send type of application in the first place.
1) If the message is that important, you will want to ensure that any user who logs on within a certain time frame of the message being sent will still receive it. You cannot do this sensibly with a net send type application.
2) Any process which polls devices will fail to identify them all at some point. The network could be down or just congested. A firewall could be blocking the poll traffic. The polled service may be temporarily unresponsive.
Consider the case when you have a problem affecting all your users and they are swaping the support desk with calls. You might want to send a message somthing like:
The corporate network is experiencing intermittent short outages caused by a failing router. The failing switch will be replaced at 13:30. Please do not log a fault call unless you experience problems after this time
Now, if the fault is intermittent there is a chance that it is going to blow away many of your checks with "network unreachable" or a similar error.
If the clients are polling however, there is a much better chance that they will manage to pick up the message on one of their polls.
