Every registered domain name has at least two Name Server records that show where it is hosted i.e. by using these records you point your Internet domain to the servers of a particular website hosting company. This way, you have both your site and your emails handled by the same company. On the lower level of the Domain Name System (DNS), nevertheless, there is a variety of other records, for example A and MX. The first one reveals which server deals with the site for a given domain name and is always an IP address (18.104.22.168), while the second one shows which server deals with the e-mails and is always an alphanumeric string (mx1.domain.com). As an example, any time you enter a domain address in your web browser, your request is sent 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 if 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 you could have your site and your emails with 2 different companies if you'd like.