Here is the scoop . . . I can send messages to accounts that reside on my Exchange servers and to external accounts I am not hosting. If I try to send messages to accounts that reside on the Linux/Postfix server, the messages sit in the Exchange message queue. An example of one of the messages "stuck" is:
Subject: TEST @ 1937
Internet Message ID: <E3336DF928658B45AD4B60C756612AD53D5452@GEMWIN0000>
From Address: email@example.com
Size (KB): 5
Message Source Name: SMTP:Default Server0
Source IP: 192.168.217.10
Date Received: 5/19/2013 9:11:09 PM
Expiration Time: 5/21/2013 9:11:09 PM
Last Error: A local loop was detected.
Queue ID: Server0\Submission
Here are my send connector settings:
Address Space - SMTP, *, 1
Network - Use domain name system (DNS) "MX" records to route mail automatically & Use the External DNS Lookup settings on the transport server
Source Servers - The private IP addresses of my two Exchange servers.
Thank you for your time,