Every single registered domain has no less than 2 Name Server records which show where it is hosted i.e. by using these records you direct your Internet domain to the servers of a certain hosting company. That way, you have both your site and your e-mails handled by the same company. On the lower level of the Domain Name System (DNS), nevertheless, there are lots of other records, for instance A and MX. The former shows which server handles the site for a given Internet domain and is always an IP address (220.127.116.11), while the latter reveals which server manages the e-mails and is always an alphanumeric string (mx1.domain.com). As an example, when you enter a domain name in your browser, your request is sent through the global DNS system to the provider whose NS records the domain address uses and from there you may be sent to the servers of another provider if you have set an IP address of the latter as an A record for your domain address. Having separate records for the site and the emails means that you could have your site and your emails with 2 different companies if you'd like.