Internet Message Access Protocol is the process of using your client to store email? on a supported account including folders, and email messages. This is intended to allow you to not have to worry about hosting your email if your computer should have a failure. Also, if you use multiple devices for your email, having IMAP will allow you to use all of the resources. Most email providers can support IMAP, but some may only do web login which is not ideal. You should always be able to have the choice of using your email client rather than using their webmail login system.