Every single registered domain name has a minimum of two Name Server records that show where it is hosted i.e. by using these records you point your domain address to the servers of a particular website hosting provider. In this way, you have got both your website and your emails managed by the exact same provider. On the lower level of the Domain Name System (DNS), on the other hand, there are a number of other records, like A and MX. The first one shows which server handles the website for a given domain name and is always an IP address (18.104.22.168), while the second one reveals which server handles the emails and is always an alphanumeric string (mx1.domain.com). For instance, any time you type a domain address in your web browser, your request is sent through the global DNS system to the company whose NS records the domain name uses and from there you will be directed to the servers of another 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 suggests that you may have your site and your emails with two different companies if you would like.