To run IMAP-SSL on Debian you need to create a new certificate for use with imap-ssl. Follow the below instructions and you're quick up and running.

 #cd /root 
 #/sbin/lidsadm -S -- -LIDS 
 #openssl req -new -x509 -days 365 -nodes -out cert.pem -keyout key.pem 
 #cp -a key.pem imapd-server.pem 
 #cp -a key.pem pop3d-server.pem 
 #cat cert.pem >> imapd-server.pem 
 #cat cert.pem >> pop3d-server.pem 
 #cp imapd-server.pem /etc/ssl/certs 
 #cp pop3d-server.pem /etc/ssl/certs 
 #/sbin/lidsadm -S -- +LIDS 
 #/etc/init.d/stunnel-imap restart 
 #/etc/init.d/stunnel-pop3 restart