how to enable TLs encryption only ?

[JOYDEEP]

Olaf Fraczyk wrote:

[ ........... }
    
> I mean that if you want to force encryption on users you need to use
> imaps. 
> If you have imap + TLS it is up to the client to decide if it wants to
> upgrade the "clear text" connection to TLS.
> Disabling imap disallows connection of clients and sending clear text
> passwords on the wire :)
>   

Exactly here I like to know how to force imap + TLS all the time and not
only IMAP :-)