The term “hosting” does not describe one service, but a number of services that provide numerous functions to a domain. Having a site and e-mails, as an illustration, are two independent services even though in the general case they come together, so a lot of people consider them as one single service. In fact, each and every domain name has a couple of DNS records called A and MX, which show the server that manages each specific service - the first one is a numeric IP address, which specifies where the website for the domain name is loaded from, while the latter is an alphanumeric string, which shows the server that handles the e-mails for the domain address. For example, an A record would be 188.8.131.52 and an MX record can be mx1.domain.com. Every time you open a site or send an email, the global DNS servers are contacted to check the name servers that a domain address has and the traffic/message is first directed to that company. If you have custom records on their end, the Internet browser request or the email will be directed to the correct server. The concept behind using separate records is that the two services employ different web protocols and you could have your site hosted by one provider and the e-mail messages by another.