Every registered domain has at least 2 Name Server records which show where it is hosted i.e. by using these records you point your domain to the servers of a specific website hosting company. This 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 lots of other records, such as A and MX. The first one shows which server manages the website for a given domain name and is always an IP address (188.8.131.52), while the second one shows which server handles the emails and is always an alphanumeric string (mx1.domain.com). For example, any time you type a domain name in your web browser, your request is directed through the global DNS system to the provider whose NS records the domain uses and from there you may be forwarded to the servers of a different company in case you have set an IP address of the latter as an A record for your Internet domain. Having separate records for the site and the e-mails suggests that you can have your site and your e-mails with 2 different providers if you wish.