POP to APOP converter

Does somebody know if there exists a POP3 proxy, that can convert POP authenication to APOP? The reasoning behind it is, that I like (for smallish installations with dial-up internet connectivity) to have POP accounts on an external mail server, e.g. with the ISP. No user accounts on the firewall, no fetchmail, just a plain TCP-proxy. Users control when to retrieve mail. But they transmit their passwords, if they use outlook or netscape email clients. Rainer