[exim] verify = sender is failing on every domain

Hi,

I've read the FAQ's and searched the exim-users index, but can't find
the answers I'm looking for.

We are still using Exim 4.30 but I've read the latest Changelog and see
no indication that this might be a bug.

We have a simple ACL in the Mail From section:

warn
    log_message = sender domain $sender_address_domain does not exist
    !verify     = sender
    delay = 20s

This verify statement is true (i.e. domain does not exist) for nearly
every
domain, not just the fake spammer domains.

Perhaps I'm misunderstanding the documentation. We do not wish to do
callout
verification as our inbound mail server is not capable of doing outbound
smtp
calls. I simply want to check if the 'MAIL From:' domain exists
via DNS and eventually change this 'warn' to a 'deny'

Can someone point me in the right direction ?
Note, we are not using exiscan.

Thanks.