Every registered domain name has a minimum of 2 Name Server records that show where it is hosted i.e. by using these records you direct your domain address to the servers of a specific hosting company. This way, you have both your site and your e-mails handled by the exact same company. On the lower level of the Domain Name System (DNS), however, there are lots of other records, for instance A and MX. The first one reveals which server deals with the site for a given domain and is always an IP address (18.104.22.168), while the latter shows which server handles the e-mails and is always an alphanumeric string (mx1.domain.com). For instance, when 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 uses and from there you will be sent to the servers of a different provider provided you have set an IP address of the latter as an A record for your domain address. Having separate records for the website and the e-mails suggests that you could have your site and your e-mails with two different companies if you'd like.