One of 2 things is happening.
1. The firewall is blocking incoming connections on TCP/25 from exchange server2.
2. Postfix is blocking relaying by exchange server2.
Testing #1 is super easy.
Go to exchange server 2, open a command prompt and type
Code:
telnet ip.of.postfix 25
If you see the postfix SMTP banner in response, then the firewall is letting you through. If no response is seen and it eventually times out, then the firewall is blocking you.
My guess is the firewall is blocking you.
To test #2, execute
Code:
postconf mynetworks mynetworks_style
If mynetworks_style is not blank, then mynetworks is ignored. If mynetworks_style is set to subnet, and the exchange server2 is on the same subnet as the postfix server, then postfix is not blocking it.
If mynetworks_style is empty, then focus on mynetworks. If it's set to your entire LAN ip network "mynetworks = 192.168.0.1/24", then postfix isn't denying relaying. If it's set to "mynetworks = 192.168.1.7/32", that means only that ip can relay email thru postfix.
Let us know what you find.
Cheers,
Pablo