Every domain that is registered and hosted has quite a lot of DNS records - some of them are set up automatically when you host a domain, others can be set up by hand if necessary. For instance, the A record of a domain name is its IP address i.e. this record shows where the web site is located; the MX records reveal where the emails are managed, while using an SRV record you can use a domain name for unconventional purposes, including a Voice-over-IP service. Being able to set up and modify certain records allows you to have different services with different companies if, for illustration, your present host provides dependable web hosting, but has difficulties with the email service, or you simply prefer to get a particular service from a specific company. Even though you should be able to create and modify these records freely and without any limits as you own a given domain name, many companies charge extra to give you this option.