Every registered domain name has at least two Name Server records that show where it is hosted i.e. by using these records you direct your Internet domain to the servers of a specific hosting company. In this way, you've got both your website and your e-mails managed by the very same provider. On the lower level of the Domain Name System (DNS), on the other hand, there are a number of other records, for example A and MX. The former shows which server deals with the site for a given domain name and is always an IP address (188.8.131.52), while the second one reveals which server handles the emails and is always an alphanumeric string (mx1.domain.com). As an example, when you enter a domain in your web browser, your request is directed through the global DNS system to the provider whose NS records the domain name 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 independent records for the site and the emails means you could have your website and your e-mails with two different companies if you'd like.