Each registered domain has at least 2 Name Server records which show where it's hosted i.e. by using these records you point your Internet domain to the servers of a specific web hosting provider. In this way, you have got both your site and your e-mails handled by the same provider. On the lower level of the Domain Name System (DNS), however, there are lots of other records, for example A and MX. The first one reveals which server handles the website for a given domain address 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 instance, any time you type a domain address in your browser, your request is directed through the global DNS system to the provider whose NS records the domain address uses and from there you will 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 domain address. Having different records for the site and the emails means that you may have your website and your e-mails with two different providers if you'd like.