[Exim] 451 error, can't find the problem

I'm having a problem with a particular user account that can't receive
mail from the outside, but local deliveries work fine.

220 frame.pinchaser.com ESMTP Exim 3.13 #2 Mon, 22 May 2000 17:01:39 -0400
helo mewl.net
250 frame.pinchaser.com Hello carrydown.lan.pinchaser.com [10.254.33.107]
mail from: chaser@???
250 <chaser@???> is syntactically correct
rcpt to: dog@???
451 Cannot check <dog@???> at this time - please try later

% exim -bt dog@???
dog@???
deliver to dog in domain mewl.net
director = localuser, transport = local_delivery


I've checked everything that I can think of on the account. Nothing is
logged about the transaction in either mainlog or rejectlog.