When I successfully send message from web page I want to notify user by window that the message was successfully sent..How

The problem is that I have some requiredfieldvalidators on page and I can't just do onclientclick=return confirm("some message")...

I tried also with ConfirmButtonExtender but it doesn't care for RequiredFieldValidators it executes on every time on button click event...

 

I want if Page.isValid I want to notify user that message is succesfully sent...How to do that..

if Page.isValid(all required fiels validators are valid) and in sc.SendCompleted event handler i want to notify user by ConfirmButtonextender that message is successfully sent...How??????
...