Every single registered domain has at least 2 Name Server records which show where it's hosted i.e. by using these records you point your domain address to the servers of a certain website hosting company. In this way, you have got both your site and your emails managed by the same service provider. On the lower level of the Domain Name System (DNS), nevertheless, there are a number of other records, for example A and MX. The former reveals which server handles the site for a given domain name and is always an IP address (18.104.22.168), while the latter shows which server manages the emails and is always an alphanumeric string (mx1.domain.com). As an example, when you enter a domain address in your browser, your request is directed through the global DNS system to the company whose NS records the domain uses and from there you may be sent to the servers of a different service provider if you have set an IP address of the latter as an A record for your domain address. Having independent records for the website and the emails means that you could have your website and your e-mails with two different companies if you'd like.