SA whitelist only alternative

Between these forums, the SpamAssassin (SA) irc.freenode channel, and the
SA website, it seems that SA can’t do “deliver only if on whitelist”.

So, is there software I can use here on DH, instead of or in addition to SA, that
will only deliver mail that meets whitelist qualification?

(I am quite surprised that SA doesn’t offer this feature.
Seems like a no brainer to me)