You mix up spamfilter and postfix whitelists here. The postfix whitelist is not related to amavisd/ spamassassin, Postfix whitelist is used when you block e.g. mails with RBL's in postfix and you want to whitelist some addresses from these rbl blocks.
Emails are scanned for spam and marked as spam by amavis/spamassassin. Amavisd has its own white and blacklists, foiund in the spamfilter section.