IMAP Internet Message Access Protocol

The Internet Message Access Protocol or IMAP is one of two of the most prevalent Internet standard protocols for e-mail retrieval, the other being POP3. Virtually all modern e-mail clients and servers support both protocols as a means of transferring e-mail messages from a server, such as those used by Gmail, to a client, such as Mozilla Thunderbird and Microsoft Outlook.

Many implementations of webmail also use IMAP to retrieve e-mail message from a server and display them within a web browser, making the use of this protocol transparent to the user.

Extract on loan from Wikipedia...http://en.wikipedia.org/wiki/Internet_Message_Access_Protocol