Every registered domain name has at least two Name Server records which show where it's hosted i.e. by using these records you direct your domain to the servers of a particular hosting provider. This way, you've got both your site and your emails handled by the very same provider. On the lower level of the Domain Name System (DNS), on the other hand, there are lots of other records, such as A and MX. The first one reveals 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 handles the emails and is always an alphanumeric string (mx1.domain.com). For example, whenever you type a domain in your Internet browser, your request is directed through the global DNS system to the provider whose NS records the domain name uses and from there you will be forwarded to the servers of a different company provided you have set an IP address of the latter as an A record for your Internet domain. Having different records for the website and the e-mails means that you can have your site and your emails with two different companies if you would like.