The Spamfilter → White/Black Lists are where you can configure whitelist ("always allow") and blacklist ("always block") options for the VPOP3 spam filter
If a word or address is in both the Whitelist and Blacklist, then, by default they will cancel each other out. Precedence can be set by altering the list check rule weights. For instance, if you want the whitelist to take precedence then you can set the whitelist rule weight to a bigger negative number than the blacklist rule weight is positive, such as setting the whitelist weight to -100 and the blacklist weight to 50. That means that if an address is in both lists, the blacklist will contribute 5000 to the final score and the whitelist will contribute -10000, meaning that the final score will be -5000, which will be passed through the filter as not spam.
The same can be done for the WhitelistWords and BlacklistWords rules.