Each registered domain has a minimum of two Name Server records that show where it is hosted i.e. by using these records you point your domain address to the servers of a specific website hosting company. That way, you have got both your site and your e-mails handled by the very same company. On the lower level of the Domain Name System (DNS), on the other hand, there are a number of other records, like A and MX. The former shows which server manages the site for a given domain address and is always an IP address (220.127.116.11), while the latter indicates which server handles the emails and is always an alphanumeric string (mx1.domain.com). As an illustration, when you enter a domain address in your Internet browser, your request is directed through the global DNS system to the provider whose NS records the domain address uses and from there you may be sent to the servers of another company if you have set an IP address of the latter as an A record for your domain name. Having separate records for the website and the emails means you can have your website and your e-mails with 2 different providers if you'd like.