First off, make sure you've applied the qmail DNS patch. I have put a copy here:
http://home.atc.no/~floyd/djb-patches/In case you're unsure how to apply the patch, here's how:
1. Stop qmail
2. Go to the qmail source directory and download the patch file
3. Run "patch < qmail-dns.patch"
4. Run "make clean" to remove what you compiled before
5. Run "make setup check" to recompile and reinstall qmail
6. Start qmail
Next, make sure DNS is actually working. This may seem too obvious to mention, but check it anyway... Verify that your /etc/resolv.conf file points to your ISP's DNS servers, and that they are in fact up and running.
Finally, several versions of libdns are broken. If it still doesn't work, try updating glibc. As an example, here is the exact procedure for a RH Linux 9 server:
1. Download the following packages:
glibc-2.3.2-27.9.7.
i686.rpm
glibc-common-2.3.2-27.9.7.i386.rpm
glibc-devel-2.3.2-27.9.7.i386.rpm
glibc-utils-2.3.2-27.9.7.i386.rpm
NOTE: It is CRITICAL that you download the correct version of glibc for your architecture, or things will break horribly!!
2. Stop qmail
3. Run "make clean" to remove what you compiled before
4. Run "make setup check" to recompile and reinstall qmail
5. Start qmail
