Each registered domain has at least two Name Server records that show where it's hosted i.e. by using these records you point your domain address to the servers of a specific hosting company. That way, you have both your website and your emails handled by the same service provider. On the lower level of the Domain Name System (DNS), however, there is a variety of other records, like A and MX. The first one reveals which server manages the website for a given Internet domain and is always an IP address (18.104.22.168), while the latter shows which server deals with the emails and is always an alphanumeric string (mx1.domain.com). As an illustration, when you type a domain name in your Internet 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 sent to the servers of another provider provided 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 e-mails means that you can have your website and your e-mails with two different providers if you'd like.