Each and every domain that's registered and hosted has a lot of DNS records - some of them are created automatically when you host a domain, others can be set up manually if required. For example, the A record of a domain address is its IP address i.e. this record reveals where the website is situated; the MX records show where the emails are handled, while through an SRV record you can use a domain name for unconventional purposes, for instance a Voice-over-IP service. The ability to set up and modify certain records allows you to have different services with different companies if, for instance, your current host provides dependable web hosting, but has problems with the email service, or you simply prefer to get a specific service from a particular company. Even though you should be able to create and edit these records freely and with no limits as you own a given domain, some companies charge extra to give you this option.