The IMAP (Internet Message Access Protocol) is an application layer Internet Protocol for access to email.
The IMAP enables users to rich possibilities for work with mail boxes located in the central server. The mail program which uses this protocol gets access to a store of correspondence in a server so as if this correspondence is located on a receiver's computer. One can manipulate e-mails from a user (client) computer without the need of constant forwarding from a server and back of files with a full content of letters.
The POP3 is the alternative protocol for collection of messages from a mail server.