The word “hosting” does not describe one service, but a set of services that offer various functions to a domain. Having a website and e-mails, for example, are two independent services though in the general case they come together, so most people think of them as one single service. The truth is, each domain name has a number of DNS records called A and MX, which show the server that deals with each specific service - the first one is a numeric IP address, which identifies where the website for the domain address is loaded from, while the second one is an alphanumeric string, which shows the server that handles the e-mails for the domain name. As an illustration, an A record would be 126.96.36.199 and an MX record would be mx1.domain.com. Every time you open a website or send an email, the global DNS servers are contacted to check the name servers that a Internet domain has and the traffic/message is first directed to that company. In case you have custom records on their end, the browser request or the e-mail will then be forwarded to the correct server. The concept behind working with separate records is that the two services use different web protocols and you may have your website hosted by one company and the e-mails by another.