gentoo-overlay/mail-filter/spamassassin/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
  <!-- maintainer-needed -->
  <use>
  <flag name="qmail">Build qmail functionality and docs</flag>
  <flag name="bayes">
    Require a database (MySQL, SQLite, Postgres, or BerkDB) backend to
    enable the Bayesian filtering database.
  </flag>
</use>
</pkgmetadata>