Before actually using it, it is necessary to prepare a word database.

1. The word contained in clean mail is counted.

  $ bsfilter --add-clean ~/Maildir/cur/*

 or

  $ cd ~/Maildir/cur/ ; ls | xargs bsfilter -c

2. The word in spam is counted.

  $ bsfilter --add-spam ~/Maildir/.spam/cur/*

 or

  $ cd ~/Maildir/.spam/cur/ ; ls | xargs bsfilter -s

3. A database is updated for every word.

  $ bsfilter -u