Each registered domain name has a minimum of two Name Server records that show where it's hosted i.e. by using these records you direct your domain address to the servers of a specific web hosting company. In this way, you've got both your website and your emails handled by the very same service provider. On the lower level of the Domain Name System (DNS), nevertheless, there are lots of other records, such as A and MX. The former shows which server deals with the site for a given domain address and is always an IP address (18.104.22.168), while the second one indicates which server manages the emails and is always an alphanumeric string (mx1.domain.com). As an example, any time you type a domain in your Internet browser, your request is sent through the global DNS system to the provider whose NS records the domain address uses and from there you will be directed to the servers of a different company in case you have set an IP address of the latter as an A record for your domain address. Having different records for the site and the e-mails suggests that you could have your site and your e-mails with two different companies if you wish.