When you add a domain name as hosted in some account, you usually set a pair of Name Servers to direct it to that particular service provider. On their end, 3 records are created automatically when the domain is added - one A record and two MX records. The former is a numeric address, or IP address, that “tells” the domain address where its site is, while the other two are alphanumeric and they reveal the server that manages the e-mails for that particular domain. The site and the e-mail hosting are typically regarded as one thing, while they are in reality two different services. Having independent records for them will enable you to have them with different companies if you want. As an example, some new provider may have fantastic uptime for your website, but you may not want to switch your e-mail messages from your current host and by using an A record to point the domain to the former and MX records to have the e-mails with the second, you can get the best of both providers. These records are checked when you want to open a site or send an email - in any case, the company whose name servers are used for the Internet domain is going to be contacted to retrieve the A and MX records and if you've set records different from their own, the right web/mail server will then be contacted and you'll see the needed site or your email is going to be delivered.