I posted this problem as an exim bug, but it was immediately dismissed
because the MTA rejection response indicates a temporary problem, so
apparently retrying 4 more times inside a second to different IP addresses
for the same domain is deemed acceptable behavior rather than waiting a
normal retry delay. If it was a connection failure rather than a message
rejection, I'd understand, but I have no experience or standing to argue
otherwise. Apparently it's not up for consideration as a candidate for a
configuration option either given the totality of the dismissal.
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