Postfix & DNS Problem Help

I have a problem with postfix, is not sending emails :

this is from the mail.log :

postfix/smtp[30100]: 597E529C0FE1: to=<d1234@yahoo.com>, relay=none, delay=38985, delays=38985/0.01/0/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=yahoo.com type=MX: Host not found, try again)

postfix/smtp[30098]: 5FCBA29C1032: to=<h1234@yahoo.com>, relay=none, delay=27875, delays=27875/0/0/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=yahoo.com type=MX: Host not found, try again)

postfix/smtp[30099]: 5162829C1053: to=<s1234@ukr.net>, relay=none, delay=22725, delays=22725/0/0/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=ukr.net type=MX: Host not found, try again)

 

Seems that the MTA can't lookup any domains. Check the DNS settings for the server running the MTA. What if you do something like "dig yahoo.com MX"?

 

looks like your dns of your ISP is down. try pinging. Those mails wont go until it resolves

 

Yeah, take a look at your DNS. yahoo.com definitely exists so you have a problem with your DNS configuration.

 

yes is a problem with the dns, now is fixed , thank you guys