Refusing connections when START_TLS is not sent

[Pierre Moermans <pmoermans@linuxmail.org>]

Dear list,

As far as I understand, clients using the START_TLS instruction must do
so on the standard (PLAIN text) port, usually, the port 389.
I've done that, and it worked fine.

Now, I would like to refuse PLAIN text communication when the START_TLS
command is not sent by the client. I've been googling for a while with
no success.
Does anybody know how to do that ?

Thanks a lot

--
Pierre