Retrieve mail contact list

Hello.


I dont really know where to put this question, So I'l go to the closest place familiour.

Do you know that Facebook or MySpage thing you have when you sign up and it asks you to give your email address and your email password?

and then, an automatic procidiour goes in to the person who has signed up and go over his mail list and sends a mail to it?

how is it done? is it an object that retreives the mailing list? is it a code?
anyone knows?

thank you.

why noone answers?
please.