[tor-relays] Received abuse complaint - how did this happen?

Today my ISP informed me that an abuse complaint had been lodged against me by spamcop.net. I looked at the report and my IP is indeed in it. It seems like a valid complaint. My question, though, is how did this happen? I'm using the Reduced Exit Policy as shown here: https://trac.torproject.org/projects/tor/wiki/TheOnionRouter/ReducedExitPoli... Neither SMTP nor SMTPS are among the ports accepted as exit ports. Anyone have any thoughts as to how my Tor config can be used to transmit spam? Thanks.