hi. I am running qmail in my office. today it stopped sending emails to yahoo and some other domains at the same time although it was sending and receiving mails to gmail and hotmail without any problem. Even the mails from yahoo were being received properly. when i checked the current mail log, the mail error was shown and the error was "CNAME lookup failed temporarily" After searching google and internet temporary solution was found by making a manual entry of one of the yahoo server in /var/qmail/control/smtproutes but this is not the permanent solution. I want to eradicate this problem for ever. anyone help please

Maybe it's the name server you're using that somehow fails to resolve yahoo.
Add as the fist nameserver entry in /etc/resolv.conf opendns:
and try again

Regards

and make sure that /etc/resolv.conf is readable to other users:
# ls -l /etc/resolv.conf
-rw-r--r-- 1 root root 0 2011-01-15 07:44 /etc/resolv.


also make sure that the firewall is not blocking the port 53


good luck