Each registered domain has no less than 2 Name Server records that show where it is hosted i.e. by using these records you direct your domain name to the servers of a specific hosting company. This way, you have both your site and your emails handled by the same provider. On the lower level of the Domain Name System (DNS), nevertheless, there are lots of other records, for instance A and MX. The former reveals which server deals with the website for a given domain name and is always an IP address (18.104.22.168), while the latter indicates which server handles the e-mails and is always an alphanumeric string (mx1.domain.com). For instance, any time you type a domain address in your browser, your request is forwarded through the global DNS system to the company whose NS records the domain uses and from there you may be directed to the servers of a different provider in case you have set an IP address of the latter as an A record for your domain address. Having independent records for the site and the e-mails means that you may have your website and your emails with 2 different providers if you would like.