All further mail processing is done locally on the client computer. In offline mode, a user simply fetches and sends mail in batches, disconnecting from the network to work with his or her messages. In other words, users download all of their mail to a local machine, and the mail is deleted immediately from the server. Unlike POP, IMAP is designed to support all three modes of operation in a single protocol, making it much easier for e-mail software developers to address the needs of all types of users. Although POP enables its clients to manipulate a message's data in many ways locally, IMAP offers considerable flexibility on the server end as well, enabling hierarchical storage and message retrieval that's more selective.
POP provides only a single in-box folder for each user on the server.
And the protocol supports multiple levels of mailboxes so that users can organize their messages even further. These mailboxes can easily be deleted, renamed, or moved by the user. Another advantage of IMAP is its ability to keep track of message-status information. General flags can mark the messages that one has already read, and user-defined flags can be used to attach personal meaning to messages. Using IMAP's added flexibility at the server end, organizations can create sophisticated server implementations to help improve workflow and distribute information.