The SORBS blacklist is widely known for extremely high false positives as well as attempting to extort users the have listed.

SORBS also requests a $50 "fine" be paid to the legal defense fund of a spammer to be delisted. This is basically using extortion to be removed from their list, regardless of the reason you are listed.

I would suggest that the recepient stop using the SORBS blacklist.

I have also requested removal from SORBS, but I do not know when/if it will happen.