[Exim] what does that mean?

We have a local mailer (mail.dff.local=172.16.1.2)
and a remote mailer with an extern and an intern interace (at
kaahless.dff.local=172.16.2.1)

Now we relay to our local mailer which then is supposed to
hand it out to our remote mailer:

outgoing_smtp:
driver = domainlist
transport = remote_smtp
route_list = "* kahless.dff.local bydns_a"

But our remote mailer refuses the messages:

connection from [172.16.1.2] refused (172.16.1.2 does not match any IP
address for kahless.dff.local)

Is that a DNS setup problem?!?
--
Torsten