SORBS is a horrible blacklist to use. Just do a quick google search on them and you will find a hundred reasons to not use their blacklist and use some of the more reputable ones out there. I could elaborate for you but after enough digging you will see what I mean. One of our customers has a client that was using sorbs and blocking all of their emails. After a week or so of back and forth with their admin, I convinced him to quit using SORBS. Reason being SORBS blocked an entire netblock at GoDaddy because of one report on one IP address (not ours ) and would not unblock without payment.
Anyway, if your using SORBS, save yourself some headaches and just quit.