Every single registered domain has at least 2 Name Server records that show where it's hosted i.e. by using these records you point your domain to the servers of a particular hosting provider. In this way, you have both your website and your e-mails handled by the exact same company. On the lower level of the Domain Name System (DNS), nevertheless, there is a variety of other records, for instance A and MX. The first one reveals which server manages the website for a given domain 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). As an illustration, any time you type a domain in your browser, your request is sent through the global DNS system to the provider whose NS records the domain uses and from there you could be sent to the servers of another service provider if you have set an IP address of the latter as an A record for your Internet domain. Having independent records for the site and the emails means you may have your website and your emails with two different companies if you would like.