I thought I had my exchange 2010 server tightened down. But I checked my queues and there were a few, about 20, messages in there with weird email address and a blank 'From' field. Here are the details of one of the messages:
Subject: Undeliverable: An E-card from your friend.
Internet Message ID: <email@example.com>
From Address: <>
Size (KB): 11
Message Source Name: DSN
Source IP: 255.255.255.255
Date Received: 8/31/2012 9:37:48 AM
Expiration Time: 9/2/2012 9:37:48 AM
Last Error: 451 Cannot connect to domain:123greetings.com - psmtp
Queue ID: my-server\177856
It looks like they're relaying thru me, but I don't know how. My firewall is setup to only accept SMTP from Postini address range. How can I track down who is sending these messages?