We have repeatedly been blacklisted by Spamhaus.org and other "anti-spam" associations and I'm having a really hard time figuring out why. The only information we are able to obtain is which of our IP addresses were blacklisted. I would really like to see the emails that supposedly are coming from our network but I am unable to find out how to get this info. Since we have multiple ISP's and multiple IP addresses we can easily fix the problem until the blacklist is removed but I would like to know why/how this is happening.
We have done the following:
1. Configured inbound/outbound policies on our firewall to only allow traffic from our Exchange Server and our anti-spam appliance (Barracuda) on port 25. Every other device is restricted from using port 25.
2. The Barracuda is configured to only allow outgoing mail from our Domain. I can see a lot of emails that seem to be trying to send out but the Barracuda blocks them. This seems the most troubling to me because I am not sure how another device (external) would use our Barracuda to try and send email.
3. Obviously have anti-virus/spyware actively running on all our PCs.
Thanks for any advice you can give.