Every domain that's registered and hosted has lots of DNS records - some of them are created automatically when you host a domain, others can be set up manually if required. As an example, the A record of a domain name is its IP address i.e. this record reveals where the web site is situated; the MX records show where the emails are stored, while with an SRV record you can use a domain name for unconventional purposes, like a Voice-over-IP service. The ability to create and modify certain records permits you to have different services with different providers if, for instance, your current host provides stable web hosting, but has issues with the e-mail service, or you simply prefer to get a specific service from a specific company. Though you can set up and modify these records freely and with no restrictions as you own a given domain address, many companies charge extra to give you this option.