The term “hosting” doesn't describe a particular service, but a set of services that provide numerous functions to a domain address. Having a website and e-mails, as an illustration, are two independent services although in the general case they come together, so many people consider them as one single service. In reality, every single domain name has a number of DNS records called A and MX, which show the server that manages each particular service - the former is a numeric IP address, that specifies where the website for the domain name is loaded from, while the latter is an alphanumeric string, which shows the server that deals with the e-mails for the domain name. For instance, an A record can be 123.123.123.123 and an MX record can be mx1.domain.com. Whenever you open a site 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 forwarded 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 concept behind employing separate records is that the two services work with different web protocols and you may have your site hosted by one company and the e-mail messages by another.