Web Forms :: How To Get All Contacts From Another Mail Engine To List

I am developing a website in asp.net using c#.net, here in my website there is registration option, so if any user who wanted to register with my site needs to fill the registration form and clicks on submit button. After that he needs to login right. After login i need to give them an option to send invitation to their friends contact mails, these mail addresses may be from their gmail or yahoomail whatever mail engine they want, i need to ask them to enter his mail address(from where they want to import all contacts) and password, as soon as he enters the info, a list of mail addresses each one preceding a check box should get displayed in my asp.net page where they logged-in so that he can select desired mail addresses from the list and send an invitation to those selected mails. Above all check boxes i need a check box when he clicks on it all the mails in the populated list must be selected and should un-check all if he un-checks that topmost checkbox.

For a clear understanding here i am giving a site [URL], register with it if you have time, i gave it to just make it more clear for what functionality i have been looking for.