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