Every single 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 name to the servers of a particular hosting provider. That way, you have both your site and your emails managed by the exact same provider. On the lower level of the Domain Name System (DNS), nevertheless, there are a number of other records, such as A and MX. The former shows which server handles the website for a given domain name and is always an IP address (18.104.22.168), while the second one indicates which server handles the emails and is always an alphanumeric string (mx1.domain.com). As an illustration, when you type a domain address in your Internet browser, your request is directed through the global DNS system to the provider whose NS records the domain name uses and from there you could be forwarded to the servers of a different service provider in case you have set an IP address of the latter as an A record for your domain. Having separate records for the website and the emails means you can have your site and your e-mails with two different providers if you would like.