The definition of “hosting” does not describe just one service, but a set of services that offer a variety of functions to a domain address. Having a website and emails, for example, are two separate services although in the general case they come together, so most people consider them as one single service. The truth is, every single domain name has a several DNS records called A and MX, which show the server that handles each specific service - the first one is a numeric IP address, that defines where the website for the domain is loaded from, while the latter is an alphanumeric string, which shows the server that deals with the emails for the domain address. For example, an A record can be 220.127.116.11 and an MX record is 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 has and the traffic/message is first directed to that company. In case you have custom records on their end, the Internet browser request or the e-mail will then be forwarded to the correct server. The reasoning behind working with separate records is that the two services use different web protocols and you could have your website hosted by one provider and the e-mail messages by another.