The word “hosting” does not describe a single service, but a variety of services that provide numerous functions to a domain. Having a site and emails, as an example, are two independent services although in the general case they come together, so most people consider them as one single service. In reality, each and every domain has a number of DNS records called A and MX, which show the server that handles each particular service - the former is a numeric IP address, which defines 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 emails for the domain address. As an example, an A record is 123.123.123.123 and an MX record would 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 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 sent to the correct server. The concept behind employing separate records is that the two services employ different web protocols and you may have your site hosted by one company and the e-mail messages by another.