Last problem with postfix

I managed to get everything now if sending email arrives but I have a problem with fqdn I did not understand what I have to put it returns this in the logs

[code:1]Mar 27 15:55:02 localhost postfix/qmgr[19939]: A94AC1B3865: from=<>, size=2999, nrcpt=1 (queue active)
Mar 27 15:55:02 localhost postfix/bounce[20470]: 62BDC1B3863: sender non-delivery notification: A94AC1B3865
Mar 27 15:55:02 localhost postfix/qmgr[19939]: 62BDC1B3863: removed
Mar 27 15:55:03 localhost postfix/smtp[20469]: A94AC1B3865: to=<root@ROOT-SERVERS.NET>,[]:25, delay=0.86, delays=0.03/0/0.66/0.17, dsn=5.0.0, status=bounced (host[] said: 553 sorry, that domain isn’t in my list of allowed rcpthosts (#5.7.1) (in reply to RCPT TO command))
Mar 27 15:55:03 localhost postfix/qmgr[19939]: A94AC1B3865: removed[/code:1]