The POP3 Remote Store is an experimental Store that behaves much the way a typical email client expects when using POP3. That is, all messages and all folders are really stored locally (in this case using the Mbox Store), and new messages are fetched from the server using the POP3 protocol.
The POP3 Remote Store is not currently distributed with Jakarta Mail, but is included in the Jakarta Mail source code in the mbox project.
XXX - still need to provide more information here.