Each registered domain name has a minimum of 2 Name Server records which show where it is hosted i.e. by using these records you direct your domain to the servers of a particular web hosting provider. In this way, you've got both your site and your emails managed by the very same service provider. On the lower level of the Domain Name System (DNS), nevertheless, there are lots of other records, for instance A and MX. The first one shows which server manages the website for a given domain name and is always an IP address (18.104.22.168), while the second one shows which server handles the emails and is always an alphanumeric string (mx1.domain.com). For instance, any time you type a domain in your Internet browser, your request is directed through the global DNS system to the company whose NS records the domain address uses and from there you may be sent to the servers of another company if you have set an IP address of the latter as an A record for your domain address. Having separate records for the site and the e-mails means that you could have your site and your e-mails with 2 different providers if you'd like.