Every domain that's registered and hosted has lots of DNS records - some of them are set up automatically when you host a domain, others can be set up manually if necessary. For instance, 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 reveal where the emails are stored, while using an SRV record you can use a domain address for unconventional purposes, for instance a Voice-over-IP service. The ability to set up and modify specific records permits you to have different services with different companies if, for illustration, your present host provides good web hosting, but has issues with the email service, or you simply prefer to get a particular service from a certain company. Though you must be able to create and modify these records freely and without any limits as you own a given domain name, a lot of companies charge extra to give you this option.