Meaning of TO_NO_BRKTS_HTML_IMG in SpamAssassin
<p>I am trying to find out what is the meaning of the flag <code>TO_NO_BRKTS_HTML_IMG</code> in SpamAssassin.</p>

<p>The provided description for it says:</p>

<blockquote>
  <p>To: lacks brackets and HTML and one image</p>
</blockquote>

<p>As far as I understand it means the mail message is in HTML format and contains only one image, but what does "To: lacks brackets" mean?</p>