It was developed by Oracle and other partners, and based on IMAP with additional enhancements for optimization in a mobile setting.
It was submitted as input to the Lemonade Profile IETF Working Group - but was not included in the resulting RFC 4550.
The protocol was designed to provide for a secure way to automatically keep communicating new messages between a server and a mobile device like a PDA or Smartphone.
It should reduce the time and effort needed to synchronize messages between the two by using an open connection that is kept alive by some kind of heartbeat.
In fact, IDLE is one of the required mechanisms for a P-IMAP server to notify the client (optional notifications are SMS or WAP Push).