The word “hosting” does not describe only one service, but a variety of services that offer numerous functions to a domain. Having a website and emails, for example, are two separate services although in the general case they come together, so a lot of people see them as one single service. The truth is, every single domain 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 specifies 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 name. For example, an A record is 18.104.22.168 and an MX record would be mx1.domain.com. Every time you open a site 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 forwarded to that company. In case you have custom records on their end, the browser request or the email will be sent to the correct server. The idea behind employing separate records is that the two services employ different web protocols and you may have your site hosted by one service provider and the e-mails by another.