function validEmail($email) {
	$isValid = true;
	$atIndex = strrpos($email, "@");
	if (is_bool($atIndex) && !$atIndex) {
		$isValid = false;
	} else {
		$domain = substr($email, $atIndex+1);
		$local = substr($email, 0, $atIndex);
		$localLen = strlen($local);
		$domainLen = strlen($domain);
		if ($localLen < 1 || $localLen > 64) {
			$isValid = false;
		} else if ($domainLen < 1 || $domainLen > 255) {
			$isValid = false;
		} else if ($local[0] == '.' || $local[$localLen-1] == '.') {
			$isValid = false;
		} else if (preg_match('/\\.\\./', $local)) {
			$isValid = false;
		} else if (!preg_match('/^[A-Za-z0-9\\-\\.]+$/', $domain)) {
			$isValid = false;
		} else if (preg_match('/\\.\\./', $domain)) {
			$isValid = false;
		} else if (!preg_match('/^(\\\\.|[A-Za-z0-9!#%&`_=\\/$\'*+?^{}|~.-])+$/',str_replace("\\\\","",$local))) {
			if (!preg_match('/^"(\\\\"|[^"])+"$/',str_replace("\\\\","",$local))) {
				$isValid = false;
			}
		}
  		if ($isValid && !(checkdnsrr($domain,"MX") || checkdnsrr($domain,"A"))) {
			$isValid = false;
		}
	}
	return $isValid;
}

E-Mail Address Validation

validation

PHP