Every single registered domain has no less than two Name Server records which show where it's hosted i.e. by using these records you direct your domain address to the servers of a particular website hosting company. This way, you have got both your site and your e-mails managed by the very same provider. On the lower level of the Domain Name System (DNS), on the other hand, there are a number of other records, for instance A and MX. The first one reveals which server manages the site for a given domain and is always an IP address (18.104.22.168), while the second one reveals which server deals with the emails and is always an alphanumeric string (mx1.domain.com). As an example, when you type 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 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 emails means that you can have your site and your e-mails with two different providers if you'd like.