Every single registered domain has no less than 2 Name Server records which show where it's hosted i.e. by using these records you point your domain address to the servers of a certain website hosting provider. In this way, you have got both your website and your e-mails handled by the same provider. On the lower level of the Domain Name System (DNS), nevertheless, there is a variety of other records, for instance A and MX. The former shows which server manages the website for a given domain and is always an IP address (18.104.22.168), while the latter indicates which server manages the emails and is always an alphanumeric string (mx1.domain.com). For instance, whenever you enter a domain in your Internet browser, your request is directed 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 provider in case you have set an IP address of the latter as an A record for your domain. Having different records for the website and the e-mails means you can have your website and your e-mails with 2 different providers if you would like.