IMAP - Internet Message Access Protocol
The Internet Message Access Protocol (commonly known as IMAP, and previously called Interactive Mail Access Protocol) is an application layer Internet protocol used for accessing e-mail on a remote server from a local client.
IMAP and POP3 (Post Office Protocol version 3) are the two most prevalent Internet standard protocols for e-mail retrieval. Both are supported by virtually all modern e-mail clients and servers, although in some cases in addition to vendor-specific, typically proprietary, interfaces.
For example, while proprietary protocols are typically used between Microsoft's Outlook client and an Exchange server and between IBM's Notes client and a Domino server, all of these products also support IMAP and POP3 allowing interoperability with other servers and clients.