Hello,
Are you able to get any feedback on the spams?
Full headers from the complainers?
Does your network listing with ARIN have an email address where people can send abuse reports?
If not, check with your ISP and see if they have reports for your IP address(es)
Is there a computer in your network that is compromised and sending spam?
If it's a small company are you able to check the traffic port by port and see who is sending outbound port 25 either by connection or at the firewall?
to Email Questions!