The definition of “hosting” does not describe just one service, but a number of services that provide a variety of functions to a domain name. Having a site and emails, for instance, are two independent services despite the fact that in the general case they come together, so a lot of people consider them as one single service. The truth is, each and every domain name 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 defines where the website for the domain address is loaded from, while the latter is an alphanumeric string, which shows the server that handles the emails for the domain name. For example, an A record would be 126.96.36.199 and an MX record is mx1.domain.com. Whenever you open a website or send an e-mail, the global DNS servers are contacted to check the name servers that a domain name has and the traffic/message is first directed to that company. When you have custom records on their end, the browser request or the email will be forwarded to the correct server. The idea behind working with separate records is that the two services use different web protocols and you can have your website hosted by one provider and the e-mails by another.