gistfile1.php

  /**
	 * Validates an email domain part
	 * 
	 * @see http://www.faqs.org/rfcs/rfc2821.html - chapter 5
	 */
	function validate_email_domain($domain, $allow_a = true, $max_cname_recursion = -1)
	{
		$flags = DNS_CNAME | DNS_MX | ($allow_a ? DNS_A | DNS_AAAA : 0);
		if (false === ($rr_list = dns_get_record($domain, $flags))) {
			throw new TPE_DNS_Exception("Could not validate domain $domain");
		}

		$have_a_record = false;

		foreach ($rr_list as $rr) {
			if ('CNAME' == $rr['type'] && $max_cname_recursion) {
				/**
				 * If a CNAME record is found instead,
				 * the resulting name is processed as if it were the initial name.
				 **/
				return $this->validate_email_domain($rr['target'], $allow_a, $max_cname_recursion - 1);
			} elseif ('MX' ==$rr['type']) {
				return true;
			} elseif ('A' == $rr['type'] || 'AAAA' == $rr['type']) {
				$have_a_record = true;
			}
		}
		/**
		 * If no MX records are found, but an A RR is found, the A RR is treated as
		 * if it was associated with an implicit MX RR, with a preference of 0,
		 * pointing to that host
		 * 
		 * This part of the specification is not used here
		 **/
		return $have_a_record;
	}