/*
Validate an email address.
Provide email address (raw input)
Returns true if the email address has the email 
address format and the domain exists.
*/
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) {
			// local part length exceeded
			$isValid = false;
		} else if ($domainLen < 1 || $domainLen > 255) {
			// domain part length exceeded
			$isValid = false;
		} else if ($local[0] == '.' || $local[$localLen-1] == '.') {
			// local part starts or ends with '.'
			$isValid = false;
		} else if (preg_match('/\\.\\./', $local)) {
			// local part has two consecutive dots
			$isValid = false;
		} else if (!preg_match('/^[A-Za-z0-9\\-\\.]+$/', $domain)) {
			// character not valid in domain part
			$isValid = false;
		} else if (preg_match('/\\.\\./', $domain)) {
			// domain part has two consecutive dots
			$isValid = false;
		} else if (!preg_match('/^(\\\\.|[A-Za-z0-9!#%&`_=\\/$\'*+?^{}|~.-])+$/', str_replace("\\\\","",$local))) {
			// character not valid in local part unless 
			// local part is quoted
			if (!preg_match('/^"(\\\\"|[^"])+"$/', str_replace("\\\\","",$local))) {
				$isValid = false;
			}
		}

	}
	return $isValid;
}

Check if an email address is valid

email

PHP