Local email addresses on the spamfilter whitelist
If you put an address on the whitelist which is also in a 'local domain', then, by default VPOP3 will ignore that when checking _incoming_ mail. This is because spammers often send spam pretending to be from the same domain as the recipient. In most cases, mail from local domains will be sent locally, not incoming, so, usually, this is a sensible rule to follow.
If you look in the messages headers of a filtered message, then VPOP3 will add a header line like:
X-VPOP3-WL: Skip Local (email.add...