The term “hosting” does not describe a single service, but several services that provide various functions to a domain name. Having a website and emails, as an illustration, are two independent services despite the fact that in the general case they come together, so most people see them as one single service. Actually, each and every domain has a couple of DNS records called A and MX, which show the server that manages each particular service - the former is a numeric IP address, that identifies where the website for the domain address is loaded from, while the second one is an alphanumeric string, which shows the server that manages the e-mails for the domain name. As an illustration, an A record would be 188.8.131.52 and an MX record is 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 web browser request or the e-mail will then be forwarded to the correct server. The reasoning behind using separate records is that the two services use different web protocols and you can have your website hosted by one service provider and the e-mails by another.