Why Whitelist?

A trained spam filter can clear your inbox of a lot of unwanted soliciations. Training that spam filter, however, can take a lot of effort and patience. To prime the pump, it is best to use a list of known good addresses, aka a whitelist. The best source of such a list is your sent mail. These are people you have sent mail to and from whom, implicitly, you are willing to receive email.

Python's mailbox module makes quick work of this otherwise tedious task. See "Why a Whitelist", first in a guide toward creating a whitelist for your email spam filter.