How do the filters work?
Generally, the filters assign and filter based on points that each message earns. We describe below, several of the settings that determine the points in the default filters.
Messages are assigned a point value depending on various factors, such as number of recipients, whether there are Blind Carbon Copy (BCC) recipients, whether the "Reply To:" address matches the "From:" address, and whether the return address is part of a domain that is notorious for spamming.Messages with a higher point value get blocked, and those with a lower value get delivered to your INBOX.
The accept and reject (white and black) lists use the "envelope address" of the message (i.e. the address the router sees) to filter mail . You can use the Spam Controls site to fine-tune your settings.