[Exim] generating a 554 error

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I want to setup exim-4.20 to reject any email it receives with a 554
error. It should do so as soon as possible in the transaction, without
regard for who the sender or recipient is.
How would I do this? With an ACL? How to generate 554 instead of 550
which is what a typical deny acl statement seems to do.
Thanks.

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