The definition of “hosting” does not describe a single service, but a number of services which provide different functions to a domain address. Having a website and emails, for example, are two separate services despite the fact that in the general case they come together, so many people see them as one single service. Actually, every single domain name has a couple of DNS records called A and MX, which show the server that deals with each specific service - the first one is a numeric IP address, that specifies where the website for the domain name is loaded from, while the second one is an alphanumeric string, which shows the server that deals with the e-mails for the domain. As an example, an A record can be 123.123.123.123 and an MX record is 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 name has and the traffic/message is first forwarded to that company. If you have custom records on their end, the Internet browser request or the e-mail will then be directed to the correct server. The concept behind using separate records is that the two services employ different web protocols and you may have your site hosted by one provider and the e-mail messages by another.