The definition of “hosting” does not describe one service, but several services which offer numerous functions to a domain address. Having a site and emails, for example, are two separate services though in the general case they come together, so most people consider them as one single service. Actually, every single domain has a several DNS records called A and MX, which show the server that deals with each specific service - the former is a numeric IP address, which defines where the site for the domain is loaded from, while the second one is an alphanumeric string, which shows the server that manages the emails for the domain. For example, an A record can be 220.127.116.11 and an MX record can be mx1.domain.com. Every time you open a website or send an email, the global DNS servers are contacted to check the name servers that a domain name has and the traffic/message is first forwarded to that company. If you have custom records on their end, the Internet browser request or the email will then be directed to the correct server. The concept behind employing separate records is that the two services use different web protocols and you can have your site hosted by one provider and the e-mails by another.