Attachment blocked by RBL

I white listed the sender domain, but the attachment of mails being sent by that domain still get blocked with reason:

Listed in RBL: Y (DNSWL_NONE)

How can I make sure that this sender domain does not get blocked by RBL?

There are several filters, working independently from one another. Here is
explained how they work: /spprotector/antispamconfiguration.php (click on
General mail whitelisting rules).
The email in the example has not been blocked because of the RBL, but
because of the bad attachment: the SA score is negative, which means Not
blocked, but the Blocked File is "Y".

To allow an attachment type from a specific domain, click on Antispam -
Advanced - File extensions, then click Tab Advanced and click Create New.
There, enter the domain to whitelist, the file extension, the Action
(allowed) etc.