Internet message access protocol (IMAP) is an alternative to POP3 as a method of retrieving email messages from a server. IMAP is used in conjunction with simple mail transfer protocol (SMTP), which allows you to send email.
Like POP3… but Different
Like POP3, IMAP allows you to have an email address with your domain name in it. But unlike POP3, IMAP keeps your email messages stored on the server even after you log in and download them to your computer.
That means you can access your IMAP-based email account from different email clients and you will be able to see your old and new messages. With IMAP, your messages are deleted from the server only when you explicitly delete them. POP3 deletes your messages from the server as soon as you download them to your computer. That limits your ability to access those messages when you're using a different device.
More Functionality
IMAP also allows you to organize your email messages into folders, which are also stored on the server. Your complete inbox is accessible from any email client, so there's no time-consuming file transfer process when you get a new computer.