The term “hosting” does not describe one service, but a variety of services which provide a variety of functions to a domain. Having a site and emails, as an illustration, are two individual services although in the general case they come together, so a lot of people consider them as one single service. In fact, each domain has a couple of DNS records called A and MX, which show the server that deals with each specific service - the first one is a numeric IP address, which specifies 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. For example, an A record is 126.96.36.199 and an MX record would be mx1.domain.com. Whenever you open a site 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 e-mail 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 may have your site hosted by one provider and the e-mails by another.