The word “hosting” does not describe a single service, but a set of services which provide numerous functions to a domain name. Having a website and emails, as an example, are two independent services though in the general case they come together, so most people think of them as one single service. The truth is, every single domain has a number of DNS records called A and MX, which show the server that handles each particular service - the first one is a numeric IP address, which specifies where the website for the domain name is loaded from, while the second one is an alphanumeric string, which shows the server that deals with the emails for the domain name. As an example, an A record would be 123.123.123.123 and an MX record can be mx1.domain.com. Each time 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. In case you have custom records on their end, the browser request or the email will then be directed to the correct server. The idea behind employing separate records is that the two services employ different web protocols and you can have your site hosted by one provider and the e-mail messages by another.