SPEWS?

It seems to me that this issue is being highly obfuscated. SPEWS
publishes a list. It is the ISP of your MAIL RECIPIENT that CHOOSES
to use it. Take up the issue with them. It was their choice to use
it - no one forced them to. I recently pointed out to the sendmail
folks that their blacklist rejection message was misleading, and I
believe they changed it.

The mail is not being blocked by SPEWS. It is being blocked/refused
as local policy by the ISP, who chooses to use the SPEWS list as
part of their decision policy.