[exim] SMTP auth with Dovecot and TLS

Hi,

I activated smtp-auth with dovecot as backend and it works nicely with
the sample in the docs.

I would like to limit the smtp-auth to TLS secured connections.
Currently also plaintext sessions get through.

I have Debian Lenny with Exim 4.69-9 installed.

Would someone have a hint how to limit?

thanks
Philipp