Mail servers are the devices that deliver your emails. They are the ones that actually grab emails from your email provider and send them to your email client (like Thunderbird). ISP Hosting: ISP hosting means that the mail server will be hosted on your ISP's network, which means that you'll have to use your ISP's email client. This is the most common type of hosting. POP3:  This type of hosting is similar to ISP hosting, except that it uses POP3 as its mail protocol. This means that you will have to open your email client and check for new mail using your ISP's mail server. IMAP: IMAP is the protocol used for accessing email. As opposed to POP3, which stores your emails on your ISP's servers, IMAP allows you to access your email from anywhere that you have an internet connection. Cloud Hosting:  Cloud hosting is the newest type of hosting. It's hosted on the cloud, which means that your email provider will store all of your emails on their server and deliver it to you. This is a very fast method of hosting, but it's also more expensive than other types