isEmail

<?php
function isEmail($value)
{
	$atom = "[-a-z0-9!#$%&'*+/=?^_`{|}~]"; // RFC 5322 unquoted characters in local-part
	$localPart = "(?:\"(?:[ !\\x23-\\x5B\\x5D-\\x7E]*|\\\\[ -~])+\"|$atom+(?:\\.$atom+)*)"; // quoted or unquoted
	$alpha = "a-z\x80-\xFF"; // superset of IDN
	$domain = "[0-9$alpha](?:[-0-9$alpha]{0,61}[0-9$alpha])?"; // RFC 1034 one domain component
	$topDomain = "[$alpha](?:[-0-9$alpha]{0,17}[$alpha])?";
	return (bool) preg_match("(^$localPart@(?:$domain\\.)+$topDomain\\z)i", $value);
}