For no reason, out of the blue, my company IP address has started to get blocked by SPAM blocking lists, most importantly, the CBL. We don't do anything like spamming at all; we don't even have the internet capacity to do that (768/128 turtle DSL). I keep delisting our IP address, but it keeps getting relisted after a few hours. I checked our network for viruses, but there are none. We don't run an open proxy; never have. I also checked our SMTP config; only recently was a new access rule added to the ISA firewall policy, but I don't think it has anything to do with this scenario; at any rate, I disabled that policy temporarily until I can figure this one out. What can I do to stop my IP from getting relisted at the SPAM blocking lists? Thanks for your help guys.