Hi Anandhi,
I don't think there is an event handler for this button, but depending on what you are trying to do, I think you should be able to write enough code before that happens that you won't need it. We have discussed sending e-mails programatically from within InfoPath several times on the forums, so search around for a little bit and see if you find anything useful.
Matt Faus / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge