[exim] Ratelimit

I have this to slow fast senders.

warn ratelimit = 100 / 1h / per_rcpt / strict
         delay     = ${eval: ${sg{$sender_rate}{[.].*}{}} -
$sender_rate_limit }s

I would like to NOT enforce this on authenticated senders since I am
slowing them elsewhere. I imagine I need to add this (!authenticated
= *) somewhere but where?

Thanks.