Every single domain name 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 created by hand if necessary. As an illustration, the A record of a domain name is its IP address i.e. this record reveals where the site is situated; the MX records reveal where the e-mails are managed, while using an SRV record you can use a domain for unconventional purposes, including a Voice-over-IP service. The ability to set up and modify specific records allows you to have different services with different companies if, for illustration, your current host provides good web hosting, but has problems with the e-mail service, or you simply prefer to get a particular service from a particular company. Although you should be able to set up and edit these records freely and with no limitations as you own a given domain address, some companies charge extra to give you this option.