OT mail spam question

I just moved my mail server to my internal office network. The IP block I've been assigned apparently used to be used for dynamic DSL users. The problem is, at some point someone used one or more of these IP addresses to send out spam, enough so that my entire Class C block is blacklisted in some database. I'm getting reject messages occasionally when I try to send someone e-mail, like so: ----- Transcript of session follows ----- ... while talking to smtp.secureserver.net.: <<< 553 66.120.4.* mail rejected due to excessive spam (Spam received from 66.120.4.201) 550 5.1.1 &lt;mike(a)sccpc.com&gt;om>... User unknown It's a very small percentage of my mail, but it's keeping me from responding to people sending me inquiries in some instances. How the *hell* do I track down what fuckwit is blacklisting my address? I appreciate the efforts people go through to thwart spam but this blanket blocking bullshit really pisses me off. -- Sellam Ismail Vintage Computer Festival ------------------------------------------------------------------------------ International Man of Intrigue and Danger http://www.vintage.org [ Old computing resources for business || Buy/Sell/Trade Vintage Computers ] [ and academia at www.VintageTech.com || at http://marketplace.vintage.org ]