Email validation (IPv4 Version)

/******************************************************************************
	Is email valid??
 
	This function verifies that the email address complies with the following
	standards:
 
	RFC 822
	RFC 1035
	RFC 2821
	RFC 2822
 
	It also ensures that the domain actually resolves.
/******************************************************************************/
 
function e_valid($email)
{
	// get position of the final @ symbol
	$index = strrpos($email, "@");
	if (is_bool($index) && !$index) return false;
 
	// split up the email address into domain and local parts
	$domain = substr($email, $index+1);
	$local = substr($email, 0, $index);
 
	// determine string length
	$l_len = strlen($local);
	$d_len = strlen($domain);
 
	// verify strings aren't too short or too long
	if ($l_len < 1 || $l_len > 64) return false;
	if ($d_len < 1 || $d_len > 255) return false;
 
	// verify that we don't start or end with a .
	if ($local[0] == '.' || $local[$l_len-1] == '.') return false;
	if ($domain[0] == '.' || $domain[$d_len-1] == '.') return false;
 
	// verify we don't have two .'s in succession
	if (preg_match('/\\.\\./', $local)) return false;
	if (preg_match('/\\.\\./', $domain)) return false;
 
	// check for disallowed characters
	if (!preg_match('/^[A-Za-z0-9\\-\\.]+$/', $domain)) return false;
	if (!preg_match('/^(\\\\.|[A-Za-z0-9!#%&`_=\\/$\'*+?^{}|~.-])+$/',
					  str_replace("\\\\","",$local)))
	{
		// check for invalid escape sequences
		if ( ! preg_match('/^"(\\\\"|[^"])+"$/', str_replace("\\\\","",$local)))
			return false;
		// check for valid DNS entries
		if ( ! (checkdnsrr($domain,"MX") || checkdnsrr($domain,"A")))
			return false;
	}
 
	// return true, the email is valid.
	return true;
}