Where the auto contacts has been stored

i am going to compose the mail for u, at the time am not add your e-mail in my contact list, i just type ur id and send a mail,after that i plan to compose a mail for same id. when type ur first letter in that To: it will display ur e-mail id.. but i didn't save that in my contact list. where that address has been store.

i replaced the .nk2 file but till i didn't get that contact..