Every registered domain name has at least two Name Server records that show where it's hosted i.e. by using these records you point your domain to the servers of a certain website hosting provider. This way, you have both your site 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, such as A and MX. The first one shows which server handles the site for a given Internet domain and is always an IP address (184.108.40.206), while the latter reveals which server handles the e-mails and is always an alphanumeric string (mx1.domain.com). For instance, when you type a domain in your Internet browser, your request is directed through the global DNS system to the company whose NS records the domain uses and from there you could be forwarded to the servers of another service provider provided you have set an IP address of the latter as an A record for your Internet domain. Having separate records for the site and the e-mails suggests that you can have your site and your emails with two different companies if you'd like.