IMAP (Internet Message Access Protocol) is an email retrieval protocol that allows email clients to access email servers in order to retrieve email messages. Email clients that use IMAP include Microsoft Outlook, Apple Mail, and Mozilla Thunderbird. IMAP has several advantages over the older POP (Post Office Protocol) email retrieval protocol. First, IMAP allows email clients to keep their email messages on the server, which means that users can access their email from any device or computer with an internet connection. Second, IMAP allows users to organize their email messages into folders on the server, which makes it easier to keep track of emails and helps prevent inboxes from becoming cluttered. Finally, IMAP supports "flag" features that allow email clients to mark email messages as read, unread, important, or spam.