The definition of “hosting” does not describe only one service, but a set of services that provide numerous functions to a domain name. Having a website and emails, for instance, are two independent services despite the fact that in the general case they come together, so a lot of people think of them as one single service. Actually, each and every domain has a number of DNS records called A and MX, which show the server that handles each particular service - the former is a numeric IP address, which defines where the website for the domain name is loaded from, while the latter is an alphanumeric string, which shows the server that handles the e-mails for the domain. As an illustration, an A record can be 22.214.171.124 and an MX record would be mx1.domain.com. Whenever you open a site or send an e-mail, the global DNS servers are contacted to check the name servers that a domain address has and the traffic/message is first directed to that company. When you have custom records on their end, the browser request or the e-mail will then be sent to the correct server. The concept behind using separate records is that the two services use different web protocols and you could have your website hosted by one company and the emails by another.