On 15 May 2009, Claudio Jeker wrote:
tcpserver, qmail-popup, qmail-pop3d and a 20 line perl script as checkpassword replacement for the POP3 case. IMAP is a bit more complex but I think dovecot and the same 20 line perl script may work.
courier-pop and courier-imap with a custom "authProg" script that roughly corresponds to this 20 line perl script is guaranteed to do POP3 and IMAP.
Regards
Oliver