We have an Exchange 2010 environment utilizing Postini for incoming e-mail. Our mail server is configured to only allow incoming e-mail from Postini so it has to get filtered rather then hitting our server directly. However one customer sending us e-mail cannot get through and gets the following e-mail back:
From: MAILER-DAEMON@messagelabs.com [mailto:MAILER-DAEMON@messagelabs.com]
Sent: Friday, February 03, 2012 12:16 PM
To: Customer Name
Subject: failure notice
This is the mail delivery agent at messagelabs.com.
I was not able to deliver your message to the following addresses.
Connected to 188.8.131.52 but sender was rejected.
Remote host said: 530 5.7.1 Client was not authenticated
Is messagelabs spam filtering somehow sending to us directly?