We manage a small network for a local real estate company. The network has a Microsoft Small Business Server 2003 with Exchange 2003 email server. We also use the Google/Postini message filtering/security service for both inbound and outbound. Port 25 is locked down so that the Exchange server can only talk SMTP to the approved IP address list of the Postini servers. All other best practices that I know of for Exchange server and email servers are enabled (recipient and sender filtering, SPF records, etc.).
The problem is that the IP address of the server keeps getting added to Barracuda Networks reputation list as "poor", resulting in bounced messages when the users try to email anyone at any company that uses the Barracuda SPAM firewalls. Here is the sample bounceback:
Arrival-Date: Tue, 26 May 2009 13:31:55 -0500
Diagnostic-Code: smtp;554 Service unavailable; Client host [na3sys009aog101.obsmtp.co
m] blocked using Barracuda Reputation; http://bbl.barracudacentral.com/q.cgi?ip=18.104.22.168
The client host listed belongs to Postini, but the IP address referenced is the IP address of the acutal Exchange server. I have requested support from Google/Postini and have not received a reply after several days. Each time the IP address is blacklisted, I follow the link to request removal and Barracuda removes it...sometimes in 5 minutes, sometimes 5 hours. I have not been able to get a response from Barracuda about what to do different to keep this from occurring every week, so I thought someone might have encountered a similar problem.