Each registered domain has no less than 2 Name Server records which show where it's hosted i.e. by using these records you direct your domain address to the servers of a certain website hosting provider. That way, you've got both your website and your e-mails handled by the very same company. On the lower level of the Domain Name System (DNS), however, there is a variety of other records, for instance A and MX. The first one reveals which server handles the website for a given domain address and is always an IP address (220.127.116.11), while the second one shows which server deals with the e-mails and is always an alphanumeric string (mx1.domain.com). As an illustration, any time you type a domain address in your browser, your request is sent through the global DNS system to the provider whose NS records the domain uses and from there you may be sent to the servers of a different provider if you have set an IP address of the latter as an A record for your domain address. Having different records for the website and the e-mails means that you could have your website and your e-mails with two different providers if you would like.