Securing Postfix?

is firewall causing this issue?

I tried the same method on other server (which is running Ubuntu), all working very well.

Fyi,

I already open port 25 for this smtp.
But still getting error after UNKNOWN

 

I don't think this is the problem, but to go sure, you can disable the firewall and try again.

 

it's not posibble to disable the firewall. Because it was build on a cisco router.

But as you know, we just need to open port 25 to do smtp right?
Maybe is there any other suggestion?

 

Yes, that's right.

I don't have any other ideas.

 

ok thank's for your help