How to obtail email registered via captive portal? And if the results can be exported

Unfortunately I cannot help you much since I'm only responsbile for checking out webites like the one about writing master dissertation at projeqt.com though I myself had to solve problems connected with routers and internet. Nevertheless, I think this thread will be more helpful to you http://forums.juniper.net/t5/Wireless-LAN/Captive-Portal-registration-page-using-email-verification/td-p/176031... good luck

First reply contained SPAM, had to be removed. 

What Controller platform/version?  I don't know that this is an available feature.