Exchange Send connector to use DNS for mail route

Hi,

I have an Exchange 2010 single box with all three roll configured.

I have configured two DNS ip on my exchange server. One is of internal DNS & second IP is Internet enabled which I NAT with public IP.

I do not have any public mx record on ISP.

I want to check mail flow from my organization to public mail e.g. hotmail, gmail etc.

I have created a Internet send connector with "Use DNS to route mail" settings.

mails are not getting out from queue. error comes. 451.4.4.0 .

Do I need to make any settings in my internal DNS.

Thanks in Advance

Anuj Gupta