[Dovecot] Q on configuring shared mboxes

Hello!

I have the following three types of mailboxes on my server:

1) Regular user mail /var/mail/<user> in mbox format
2) Suspected spam in /var/tmp/spamprobe in mbox format
3) Archived mailing list in /home/mks/mksarch in mbox format

I want the 1) to be only accessible to the respective <user>, obviously (POP3 and/or IMAP4).

I wanted the 2) to be accessible to all users -- and I want them to be able to move stuff out of it into their own mboxes (IMAP4 is enough).

I want the 3) to be accessible _read only_ to anyone, who enters the correct username/password (preferably -- without creating a special Unix account). (IMAP4 or POP3)

So far, I have only been able to achieve 1). Could someone, please, help me configure dovecot for the 2) and the 3)? Thanks!

-mi