php 检查电子邮件的函数

检查电子邮件的工作对于一些注册类的网站来说非常有必要，分享一个不错的函数。
 
代码:

<?php
function is_valid_email_address($email){ 
$qtext = '[^//x0d//x22//x5c//x80-//xff]'; 
$dtext = '[^//x0d//x5b-//x5d//x80-//xff]'; 
$atom = '[^//x00-//x20//x22//x28//x29//x2c//x2e//x3a-//x3c'. 
'//x3e//x40//x5b-//x5d//x7f-//xff]+'; 
$quoted_pair = '//x5c[//x00-//x7f]'; 
$domain_literal = "//x5b($dtext|$quoted_pair)*//x5d"; 
$quoted_string = "//x22($qtext|$quoted_pair)*//x22"; 
$domain_ref = $atom; 
$sub_domain = "($domain_ref|$domain_literal)"; 
$word = "($atom|$quoted_string)"; 
$domain = "$sub_domain(//x2e$sub_domain)*"; 
$local_part = "$word(//x2e$word)*"; 
$addr_spec = "$local_part//x40$domain"; 
return preg_match("!^$addr_spec$!", $email) ? 1 : 0; 
}