Each registered domain has no less than 2 Name Server records which show where it's hosted i.e. by using these records you point your domain name to the servers of a specific web hosting provider. This way, you have got both your website and your e-mails handled by the very same provider. On the lower level of the Domain Name System (DNS), however, there are a number of other records, for instance A and MX. The first one shows which server handles the site for a given domain name and is always an IP address (220.127.116.11), while the second one shows which server manages the e-mails and is always an alphanumeric string (mx1.domain.com). As an illustration, whenever you enter a domain address in your web browser, your request is directed through the global DNS system to the company whose NS records the domain address uses and from there you could be directed to the servers of a different provider provided you have set an IP address of the latter as an A record for your domain. Having separate records for the site and the e-mails means that you could have your site and your emails with two different providers if you would like.