Every registered domain name has a minimum of 2 Name Server records that show where it's hosted i.e. by using these records you point your domain to the servers of a specific hosting company. That way, you have both your site and your emails managed by the exact same company. On the lower level of the Domain Name System (DNS), on the other hand, there are lots of other records, for example A and MX. The first one shows which server deals with the website for a given domain address and is always an IP address (188.8.131.52), while the second one reveals which server deals with the e-mails and is always an alphanumeric string (mx1.domain.com). For instance, when you type a domain name in your web browser, your request is sent through the global DNS system to the company whose NS records the domain address uses and from there you could be directed to the servers of another service provider in case you have set an IP address of the latter as an A record for your Internet domain. Having different records for the site and the e-mails suggests that you can have your website and your emails with 2 different companies if you'd like.