IETF RFC 3691 PDF

This document defines an UNSELECT command that can be used to close the current mailbox in an Internet Message Access Protocol - version 4 (IMAP4) session without expunging it. Certain types of IMAP clients need to release resources associated with the selected mailbox without selecting a different mailbox. While IMAP4 provides this functionality (via a SELECT command with a nonexistent mailbox name or reselecting the same mailbox with EXAMINE command), a more clean solution is desirable.