Each registered domain has at least two Name Server records which show where it is hosted i.e. by using these records you point your domain to the servers of a specific hosting provider. This way, you have both your website and your e-mails managed by the exact same company. On the lower level of the Domain Name System (DNS), nevertheless, there is a variety of other records, for example A and MX. The first one reveals which server handles the site for a given domain and is always an IP address (220.127.116.11), while the latter reveals which server handles the emails and is always an alphanumeric string (mx1.domain.com). As an example, any time you type a domain address in your Internet browser, your request is directed through the global DNS system to the company whose NS records the domain uses and from there you will be sent to the servers of a different provider in case you have set an IP address of the latter as an A record for your domain name. Having independent records for the website and the emails means you can have your site and your e-mails with two different companies if you'd like.