<?php
$str = 'On 12-06-13 10:56 AM, "John Doe" <john.doe@some.tld> wrote:';
$email = preg_match('/^On [^"]*"[^"]*" <([^>]*)> wrote:$/', $str, $re) ?
$re[1] : ''; print ($email);
?>
PD9waHAKICAkc3RyID0gJ09uIDEyLTA2LTEzIDEwOjU2IEFNLCAiSm9obiBEb2UiIDxqb2huLmRvZUBzb21lLnRsZD4gd3JvdGU6JzsKICAkZW1haWwgPSBwcmVnX21hdGNoKCcvXk9uIFteIl0qIlteIl0qIiA8KFtePl0qKT4gd3JvdGU6JC8nLCAkc3RyLCAkcmUpID8gJHJlWzFdIDogJyc7CnByaW50ICgkZW1haWwpOwo/Pg==