Every registered domain has no less than two Name Server records which show where it's hosted i.e. by using these records you point your domain to the servers of a specific hosting provider. This way, you have got both your website and your e-mails managed by the exact 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 first one shows which server manages the site for a given domain address and is always an IP address (123.123.123.123), while the second one shows which server handles the e-mails and is always an alphanumeric string (mx1.domain.com). For example, any time you enter a domain in your browser, your request is directed through the global DNS system to the company whose NS records the domain address uses and from there you could be forwarded to the servers of a different service provider if you have set an IP address of the latter as an A record for your domain. Having independent records for the website and the emails means that you may have your site and your emails with 2 different providers if you'd like.