The sender is usrisk.com, an insurance company. the recipient is MY exchange server that I manage. The sender sends the email to my user, and the sender gets the message below.
the recipient is valid. the sender is in my whitelist by IP and domain.
From: Mail Delivery System [mailto:email@example.com]
Sent: Tuesday, April 26, 2011 9:06 AM
To: Elizabeth Wafer
Subject: Mail delivery failed: returning message to sender
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:
SMTP error from remote mail server after end of data:
host domain.com [65.70.xxx.xx]: 554 5.1.0 Sender denied