Every domain name which is registered and hosted has quite a lot of DNS records - some of them are created automatically when you host a domain, others can be created manually if required. For instance, the A record of a domain name is its IP address i.e. this record reveals where the website is located; the MX records reveal where the emails are stored, while through an SRV record you can use a domain address for unconventional purposes, like a Voice-over-IP service. The ability to create and modify specific records permits you to have different services with different providers if, for example, your current host provides good web hosting, but has issues with the e-mail service, or you simply prefer to get a particular service from a specific company. Though you should be able to set up and modify these records freely and with no limits as you own a given domain name, some companies charge extra to give you this option.