Very liberal PHP is valid email check.

emailcheck.php

<?php
function isValidEmailAddress($email) {

	return (
		(preg_match('/^[^\r\n\t]+@[^\r\n\t ]+\.(?i)[a-z]{2,10}$/',$email)) &&
		(count($partList = explode('@',$email)) == 2) &&
		(!preg_match('/\.{2}/',$partList[1]))
	);
}


// valid
isValidEmailAddress("my.name@somedomain.com");

// invalid
isValidEmailAddress("my.n\t\r\name@some\rdomain.com"); // \r\n\t characters bad
isValidEmailAddress("my.name@some domain.com"); // spaces in domain component
isValidEmailAddress("my.name@som@edomain.com"); // multiple "@" characters
isValidEmailAddress("my.name@som@edomain.longtld12334"); // longer than 10 characters TLD
isValidEmailAddress("my.name@some..domain.com"); // double (or more) sequential dots

What about control characters or whitespace? Look at the PHP unicode regex rules on php.net

Whitespace in the domain portion, good point - but it IS valid in the name@ part if the name is quoted.

Trying not to be too intense here with the checking :)