Every single registered domain name has a minimum of two Name Server records which show where it's hosted i.e. by using these records you direct your domain address to the servers of a specific hosting provider. That way, you have got both your website and your emails managed by the very same provider. On the lower level of the Domain Name System (DNS), nevertheless, there is a variety of other records, such as A and MX. The first one reveals which server manages the site for a given domain and is always an IP address (18.104.22.168), while the latter indicates which server manages the e-mails and is always an alphanumeric string (mx1.domain.com). For instance, whenever you enter a domain in your Internet browser, your request is sent through the global DNS system to the company whose NS records the domain name uses and from there you will be forwarded to the servers of a different service provider provided you have set an IP address of the latter as an A record for your domain name. Having separate records for the site and the e-mails means that you can have your website and your emails with 2 different companies if you would like.