Tips

General Usage

Advanced Tips

Batch Training

You could create a view that contains all your messages except your junk messages (all messages whose category isn't "Junk" and all messages not in the "Junk" folder). That way, selecting this category will enable you to train the filter with all your good emails.

Counteracting "wrong" classifications

To make the junk filter ignore a classification you made (which should rarely be necessary, because the filter can easily tolerate some noise):

Counteracting excessive classification mistakes

If you misclassified billions of emails and you simply don't know how to undo that any more, the databases reside in ~/Library/Application Support/dictionaries. Deleting the files there will make the junk filter start from scratch.