Each registered domain name has no less than 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. This way, you've got both your site and your emails handled by the very same provider. On the lower level of the Domain Name System (DNS), nevertheless, there is a variety of other records, such as A and MX. The first one shows which server manages the website for a given domain and is always an IP address (18.104.22.168), while the second one shows which server manages the emails and is always an alphanumeric string (mx1.domain.com). As an illustration, when you type a domain name in your web 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 directed to the servers of a different company 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 e-mails means you can have your website and your emails with 2 different providers if you wish.