[exim] Rejecting connections that have only IP as sender_hel…

I was searching through the lists and reading the documentation but I'm
coming up short on blocking IP only senders.

I've seen ACLs checking sender_helo_name using isip{} but that doesn't
seem to do anything for the case of a literal IP:

H=([185.17.76.25])

What's the proper way to check for the above condition and reject it?

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