[exim] Bug in DNS resolver or in DNS setup?

Hello,

I have the following problem:

2007-07-10 21:49:46 no IP address found for host mosambik.phantasia.org (during SMTP connection from [83.223.83.9]:3633 I=[195.4.92.15]:25)

I checked the DNS setup, and it looks OK to me (no lame delegation,
zones are consistent etc). It is a little uncommon that the reverse
zone contains a CNAME for a PTR record, but Exim has no trouble to find
out the hostname, so that appears to work.

I have no idea why looking up the host fails, though. Any ideas?

Michael