system not able to send mail to external address

[Wade Preston Shearer]

Within /etc/aliases on my server, I have "root" pointing at an outside address (such as "u...@external_example.com"). This means that any mail sent to root (such as my daily LogWatch emails) are forwarded to this external address. This has worked for several years. A month or two ago, I changed the address to a different address. Since then, I have had significant problems. I get returned mail emails from the Mail Delivery Subsystem (mailer daemon) stating that "the address had permament fatal errors) and that after trying for five days, the message will be deleted from queue. My first thought was that my server could not communicate with my new email providers so I ran a few tests. Using the command line mail client, I sent test messages from a non-root user's account to both this new address and to "root." Both were delivered successfully.

Here is an example of the returned emails:

__________________________________________

The original message was received at Mon, 2 Feb 2009 04:03:12 -0700
from localhost.localdomain [127.0.0.1]

  ----- The following addresses had permanent fatal errors -----
u...@external_example.com
   (expanded from: <r...@example.com>)

  ----- Transcript of session follows -----
u...@external_example.com... Deferred
Message could not be delivered for 5 days
Message will be deleted from queue
Reporting-MTA: dns; example.com
Arrival-Date: Mon, 2 Feb 2009 04:03:12 -0700

Final-Recipient: RFC822; r...@example.com
X-Actual-Recipient: RFC822; u...@external_example.com
Action: failed
Status: 4.4.7
Last-Attempt-Date: Sat, 7 Feb 2009 04:39:42 -0700

Does anyone have any idea why mail sent to root from the command line mail client would be forwarded ("expanded") to the alias email address and delivered successfully while email messages generated by scripts (such as LogWatch and Mailman) are not forwarded ("expanded")? Also, here's the other thing that is boggling my mind: why do I get the failure email but not the original email?

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