[exim] reject unauthenticated mail from local users?

Hi,

I want to reject mail where the sender email address is from my local
domain unless the sender is authenticated or the sender is in our LAN.
Rationale is that we get spam with faked local addresses and users are
less careful opening them if the recognize the sender.

In postfix I would do that using something like:

smtpd_recipient_restrictions = permit_sasl_authenticated,
permit_mynetworks, check_sender_access hash:sender_access,
reject_unauth_destination

and having "my-domain.com 554 Please authenticate first" in
sender_access

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