Every single 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 certain website hosting company. That way, you've got both your website and your e-mails handled by the same company. On the lower level of the Domain Name System (DNS), however, there is a variety of other records, like A and MX. The former shows which server handles the website for a given Internet domain and is always an IP address (18.104.22.168), while the second one indicates which server deals with the emails and is always an alphanumeric string (mx1.domain.com). As an example, when you type a domain name in your Internet browser, your request is sent through the global DNS system to the provider whose NS records the domain uses and from there you could be directed to the servers of another service provider in case you have set an IP address of the latter as an A record for your domain name. Having different 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 would like.