retorno de mensagens de servidores qmail

Trabalho com network e minha empresa esta sem receber e-mails de provedores que usam servidores Qmail. Uso um servidor domino 5.0 numa máquina windows. Os e-mails retornam assim

Hi. This is the qmail-send program at yahoo.com.
I'm afraid I wasn't able to deliver your message to the following
addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

<[email protected]>:
CNAME lookup failed temporarily. (#4.4.3)I'm not going to try again; this message has been in the queue too
long.

--- Below this line is a copy of the message.

Return-Path: <[email protected]>
Received: (qmail 18386 invoked by uid 60001); 30 Nov 2005 20:28:08
-0000
DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws;
s=s1024; d=yahoo.com.br;

h=Message-ID:Received:Date:From:Subject:To:MIME-Version:Content-Type:Content-Transfer-Encoding;

b=CtSXnBgbQJ0Tql+kbf0C4rnzXcH3TERyA0+xcS65JEUZczOEswyvqUf47TEYA89ctPQvkxoFpUiktSx+afHzz2q3kSphV1ndPC1EwUXvdE8O9obUEfuhoiGgyHz3I5xvno2OEbKcCMu7TCae6CL1MCSkDQKDRsuUDKy+eSOF/Dw=
;

O que está errado na configuração da minha rede?? Ou é algum problema do qmail??? Qualquer ajuda é bem vinda.