function is_valid_email($email, $test_mx = false)
{
	if(eregi("^([_a-z0-9-]+)(\.[_a-z0-9-]+)*@([a-z0-9-]+)(\.[a-z0-9-]+)*(\.[a-z]{2,4})$", $email))
		if($test_mx)
		{
			list($username, $domain) = split("@", $email);
			return getmxrr($domain, $mxrecords);
		}
		else
			return true;
	else
		return false;
}

E-mail validation is perhaps the most used validation in web forms, this code will validate email address and also optionally check the MX records of the domain provided in email address to make email validation more robust.

Validate Email Address

email, php, forms

PHP