Each domain which is registered and hosted has quite a lot of DNS records - some of them are created automatically when you host a domain, others can be created manually if required. As an example, the A record of a domain is its IP address i.e. this record shows where the web site is located; the MX records reveal where the e-mails are managed, while through an SRV record you can use a domain for unconventional purposes, including a Voice-over-IP service. The ability to create and modify specific records permits you to have different services with different companies if, for illustration, your current host provides stable web hosting, but has difficulties with the email service, or you simply prefer to get a certain service from a certain company. Although you must be able to set up and edit these records freely and without any limitations as you own a given domain address, lots of companies charge extra to give you this option.