[Exim] starttls acl

I'm in the process of implementing secure email. I have the pop
side working with qpopper-ssl, but am having a problem with the
exim allowing a starttls connection. Reading the manual I have
found I need an acl for starttls as specified with acl_smtp_starttls. I
have no idea what I should put in the acl and the online manual is
less than helpful. Any suggestions?

Rossz