My Postfix can't send mail to other systems

my log (/var/spool/mail/info) :

Aug 11 19:03:11 cbox-hcm imapd: Connection, ip=[::ffff:192.168.100.110]
Aug 11 19:03:11 cbox-hcm imapd: LOGIN, user=nha@chinhnam.com, ip=[::ffff:192.168.100.110], protocol=IMAP
Aug 11 19:21:44 cbox-hcm postfix/qmgr[12405]: A787713A8D: from=<admin@chinhnam.com>, size=1426, nrcpt=1 (queue active)
Aug 11 19:21:44 cbox-hcm postfix/qmgr[12405]: CCDF913A97: from=<admin@chinhnam.com>, size=1354, nrcpt=1 (queue active)
Aug 11 19:21:44 cbox-hcm postfix/qmgr[12405]: 3D4C013A98: from=<admin@chinhnam.com>, size=1385, nrcpt=1 (queue active)
Aug 11 19:21:44 cbox-hcm postfix/qmgr[12405]: D972913A9A: from=<admin@chinhnam.com>, size=1400, nrcpt=1 (queue active)
Aug 11 19:21:44 cbox-hcm postfix/smtp[12534]: A787713A8D: to=<tchithanh2003@yahoo.com>, relay=none, delay=60830, status=deferred (Name service error for name=yahoo.com type=MX: Host not found, try again)
Aug 11 19:21:44 cbox-hcm postfix/smtp[12536]: 3D4C013A98: to=<daiviet@hcm.vnn.vn>, relay=none, delay=57687, status=deferred (Name service error for name=hcm.vnn.vn type=MX: Host not found, try again)
Aug 11 19:21:44 cbox-hcm postfix/smtp[12538]: CCDF913A97: to=<tchithanh2003@yahoo.com>, relay=none, delay=58181, status=deferred (Name service error for name=yahoo.com type=MX: Host not found, try again)
Aug 11 19:21:44 cbox-hcm postfix/smtp[12539]: D972913A9A: to=<tchithanh2003@yahoo.com>, relay=none, delay=11501, status=deferred (Name service error for name=yahoo.com type=MX: Host not found, try again)

Please help me to solving my problem ?
Thanks.