NDR error

greetings to all,

I have exchange 2013 run and working except two domains that i am not able to send email to.

one of them giving me NDR of

smtp.hec-group.com.tw rejected your message to the following email addresses:

smtp.hec-group.com.tw gave this error: Service unavailable

A problem occurred while delivering this message to this email address. Try sending this message again. If the problem continues, please contact your helpdesk.

Diagnostic information for administrators:

Generating server: Mail.TEST.local

 smtp.hec-group.com.tw Remote Server returned '500 5.0.0 Service unavailable'

Original message headers:

Received: from Mail.TEST.local (10.0.5.4) by Mail.TEST.local (10.0.5.4) with

 Microsoft SMTP Server (TLS) id 15.0.847.32; Fri, 22 Aug 2014 10:17:28 +0300

Received: from Mail.TEST.local ([fe80::bc95:26fb:eac0:be73]) by

 Mail.TEST.local ([fe80::bc95:26fb:eac0:be73%12]) with mapi id 15.00.0847.030;

 Fri, 22 Aug 2014 10:17:28 +0300

================================================================================

the other domain gave me this NDR

‏‏create by the server : Mail.TEST.localreceiving server: mx20.013net.net (194.90.9.19) Total retry attempts: 1

aaa Remote Server at mx20.013net.net (194.90.9.19) returned '400 4.4.7 Message delayed' 20/08/2014 16:28:29 - Remote Server at mx20.013net.net (194.90.9.19) returned '441 4.4.1 Error encountered while communicating with primary target IP address: "421 4.4.2 Connection dropped due to TimedOut." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts. The last endpoint attempted was 194.90.9.19:25'

i wondering if better for me implementing by using smart host in thereceiving connector

due to the fact my domain is 'new' to the 'world' ?

Thank you.