This plugin is designed to reject incoming messages at SMTP-time if their subjects are contained upon a local blacklist.
The blacklist is located in the file /etc/qpsmtpd/badsubject and consists of lines such as:
ATTENTION FUND BENEFICIARY.
DONATION CASH AID AWARD
This plugin is prone to false positives if the list of subjects is too broad, but despite this it may be useful in extremis or as an example of how to write qpsmtpd plugins.