[CentOS] Postfix problem with DNS

Today I have changed my DSL modem and problems with postfix begun. It
receives mail, but cannot send any. In logs I can read

Jun 22 19:39:53 server postfix/smtp[5040]: 9A51711FF85:
to=address at somedomain.com, relay=none, delay=12840, status=deferred (Host or
domain name not found. Name service error for name=somedomain.com type=MX:
Host not found, try again)

My resolv.conf is proper. I can ping any server, but postfix cannot see
them.
What can I do ?
Postfix 2.1.5

Best Regards
Kuba


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