Every registered domain name has a minimum of two Name Server records which show where it's hosted i.e. by using these records you direct your Internet domain to the servers of a certain hosting company. In this way, you have got both your website and your emails managed by the same provider. On the lower level of the Domain Name System (DNS), on the other hand, there is a variety of other records, for example A and MX. The former shows which server handles the website for a given domain and is always an IP address (18.104.22.168), while the latter reveals which server manages the emails and is always an alphanumeric string (mx1.domain.com). For instance, any time you enter a domain name in your web 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 directed to the servers of another company provided you have set an IP address of the latter as an A record for your domain name. Having different records for the site and the emails suggests that you could have your site and your emails with 2 different companies if you wish.