Any active domain that is added in a hosting account features a variety of records that allow it to function properly. In the typical case, the name servers (NS records) show where the domain name is hosted and they are set on the side of the registrar company, but on the lower level there are certain records set through the hosting company like A (IP address of the website/server), MX (e mail server), SRV (using a domain name for non-website purposes on a specific port number such as Voice-over-IP), and many others. With access to these records and by having the capacity to edit them, you may have your website with company A and your e-mails with company B, for example. This offers you more overall flexibility since you can choose the best provider for every single one of these services and you don't have to stick with one company. After you select a hosting company, you have to make sure that you have access to all DNS records freely because some providers have an additional fee for this function.