The definition of “hosting” does not describe only one service, but a variety of services that provide various functions to a domain address. Having a website and e-mails, as an example, are two independent services though in the general case they come together, so many people think of them as one single service. In reality, every domain name has a several DNS records called A and MX, which show the server that manages each specific service - the first one is a numeric IP address, that identifies where the site for the domain name is loaded from, while the latter is an alphanumeric string, which shows the server that deals with the e-mails for the domain address. As an illustration, an A record can be 188.8.131.52 and an MX record can be mx1.domain.com. Every time you open a website or send an e-mail, the global DNS servers are contacted to check the name servers that a Internet domain has and the traffic/message is first forwarded to that company. When you have custom records on their end, the Internet browser request or the e-mail will be forwarded to the correct server. The reasoning behind using separate records is that the two services use different web protocols and you may have your website hosted by one company and the emails by another.