Every single registered domain has a minimum of 2 Name Server records that show where it is hosted i.e. by using these records you point your domain name to the servers of a certain website hosting provider. That way, you have got both your site and your emails handled by the same company. On the lower level of the Domain Name System (DNS), on the other hand, there is a variety of other records, for example A and MX. The first one reveals which server handles the site for a given Internet domain and is always an IP address (188.8.131.52), while the latter indicates which server manages the emails and is always an alphanumeric string (mx1.domain.com). As an illustration, when you enter a domain name in your Internet browser, your request is directed through the global DNS system to the provider whose NS records the domain address uses and from there you may be directed to the servers of another company if you have set an IP address of the latter as an A record for your domain address. Having separate records for the website and the e-mails means that you could have your site and your e-mails with two different companies if you wish.