<?php
$addr = "http://otvety.mail.ru/";
$mdb = "mails.txt";
$cont = file_get_contents($addr);

preg_match_all("|\<div.+class=\"add\"\>\<a.+href=\"http:\/\/www.mail.ru\/agent\?message\&to=(.+\.ru)\"\>|i", $cont, $mail);

$fp = fopen($mdb, "r+");
fputs($fp, $mail[1]."\r\n");
fclose($fp);
?>