The term “hosting” doesn't describe a particular service, but a variety of services which provide a variety of functions to a domain. Having a site and e-mails, as an illustration, are two independent services though in the general case they come together, so many people consider them as one single service. Actually, each and every domain name has a several DNS records called A and MX, which show the server that manages each specific service - the former is a numeric IP address, which identifies where the website for the domain address is loaded from, while the latter is an alphanumeric string, which shows the server that handles the emails for the domain. For instance, an A record can be 18.104.22.168 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. When you have custom records on their end, the Internet browser request or the email will 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 can have your website hosted by one service provider and the e-mail messages by another.