The term “hosting” does not describe just one service, but a number of services that offer different functions to a domain name. Having a site and emails, as an example, are two separate services despite the fact that in the general case they come together, so most people think of them as one single service. The truth is, every domain has a several DNS records called A and MX, which show the server that handles each particular service - the former is a numeric IP address, which specifies where the website for the domain is loaded from, while the latter is an alphanumeric string, which shows the server that manages the emails for the domain name. As an example, an A record is 126.96.36.199 and an MX record would be mx1.domain.com. Each 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 directed to that company. If you have custom records on their end, the browser request or the e-mail will be forwarded to the correct server. The idea behind working with separate records is that the two services work with different web protocols and you may have your website hosted by one provider and the emails by another.