Every single registered domain name has a minimum of 2 Name Server records that show where it's hosted i.e. by using these records you point your domain address to the servers of a certain website hosting company. That way, you have got both your site and your e-mails managed by the same provider. On the lower level of the Domain Name System (DNS), nevertheless, there is a variety of other records, like A and MX. The first one reveals which server deals with the website for a given domain address 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, whenever you type a domain name in your web browser, your request is sent through the global DNS system to the provider whose NS records the domain name 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. Having separate records for the site and the emails means you may have your website and your emails with two different providers if you wish.