PHP-Code:
<?php
function check_email($email)
{
$nonascii = "\x80-\xff";
$nqtext = "[^\\\\$nonascii\015\012\"]";
$qchar = "\\\\[^$nonascii]";
$protocol = '(?:mailto:)';
$normuser = '[a-zA-Z0-9][a-zA-Z0-9_.-]*';
$quotedstring = "\"(?:$nqtext|$qchar)+\"";
$user_part = "(?:$normuser|$quotedstring)";
$dom_mainpart = '[a-zA-Z0-9][a-zA-Z0-9._-]*\\.';
$dom_subpart = '(?:[a-zA-Z0-9][a-zA-Z0-9._-]*\\.)*';
$dom_tldpart = '[a-zA-Z]{2,5}';
$domain_part = "$dom_subpart$dom_mainpart$dom_tldpart";
$regex = "$protocol?$user_part\@$domain_part";
return preg_match("/^$regex$/",$email);
}?>