Hi Nadya,

> I added an Error trapping routine to the procedure (thanks to Sergey Berezniker). It works nicely if the service is running. However, it doesn't show message if the service is not running, but still returns true.

That's because WriteFile only checks whether the content got writte, or not. In this case, it got written into a mailslot.

A mailslot behaves much like a real post box in your home. Everyone can send you a letter, but nobody can be sure you actually read it. Not even when the mail company delivers the letter to you post box, anybody can really be certain that you'll receive the letter. Someone might take it out while you are away.

Messages written into a mailslot are broadcasted. You cannot only send a message to a single machine, but to an entire group or even all machines on the network, or to multiple application on a single computer. Even if the sender could determine whether the receiver got the message, what would be the return value if half of them got it, the other half not?

In any case, technically mailslots are implmented as datagrams (UDP protocol). Unlike the TCP protocol UDP doesn't have any kind of hand-shakig, delivery-control. etc. Sending a message via UDP generates a single IP packet that might or might not reach the recipient.