STARTTLS Question

[Daniel Whelan]

I'm currently operating a Cyrus server listening in the following 
configuration, and authenticating via PLAIN/LOGIN with a saslauthd backend 
(only relevant config lines listed):

imap        cmd="imapd -U 30" listen="localhost:imap"
imaps       cmd="imapd -s -U 30" listen="imaps"
pop3s       cmd="pop3d -s -U 30" listen="pop3s"

The IMAPS and POP3S ports are for user interaction, and the IMAP port is 
for the local webmail client (which operates over apache and mod_ssl). I 
don't wish to offer any services in an unencrypted format.

My question is, can I offer the IMAP port to any client but configure it 
such that they are required to STARTTLS to communicate? This would help 
with some picky email clients that don't like to deal with the alternate 
IMAPS port properly. Thanks!

Daniel