I feel like it's all been said before, so I won't bother going in to any depth on my opinion of companies such as Netprospex. Instead, I'll just link you to their latest Spamhaus blacklisting. The entry is light on details, so I could but speculate as to what happened. But clearly, the blacklisted IP addresses 22.214.171.124 and 126.96.36.199 are now having significant issues attempting to deliver mail to Yahoo, Hotmail, Gmail, Comcast and many other ISPs. Ouch.
(Update: Two SBL entries, from the looks of it. Click on the IP addresses above to link to each.)