The term “hosting” does not describe one service, but a number of services that provide numerous functions to a domain. Having a website and e-mails, as an example, are two independent services although in the general case they come together, so most people see them as one single service. The truth is, each and every domain has a number of DNS records called A and MX, which show the server that handles each specific service - the first one is a numeric IP address, which identifies where the site for the domain is loaded from, while the second one is an alphanumeric string, which shows the server that manages the e-mails for the domain. For instance, an A record can be 123.123.123.123 and an MX record can 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 name 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 e-mail will then be sent 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 site hosted by one provider and the emails by another.