Yup. I'm using qmail as the MTA and courier IMAP allowing both secure
and insecure connections. All mail users have virtual accounts set up in
a userdb file. I've verified that the connections that should be
encrypted really are using a packet sniffer.
Maybe listing the contents of your imapd and imapd-ssl files would allow
people to provide more help.
If you did, could you please point to the documentation you used and even
be nice enough to step us through what you did.