Policies concerning the content of list traffic.
<p>Content filtering works like this: when a message is
received by the list and you have enabled content filtering, the
individual attachments are first compared to the
<a href="?VARHELP=contentfilter/filter_mime_types">filter
types</a>. If the attachment type matches an entry in the filter
types, it is discarded.
<p>Then, if there are <a
href="?VARHELP=contentfilter/pass_mime_types">pass types</a>
defined, any attachment type that does <em>not</em> match a
pass type is also discarded. If there are no pass types defined,
this check is skipped.
<p>After this initial filtering, any <tt>multipart</tt>
attachments that are empty are removed. If the outer message is
left empty after this filtering, then the whole message is
discarded. Then, each <tt>multipart/alternative</tt> section will
be replaced by just the first alternative that is non-empty after
filtering.
<p>Finally, any <tt>text/html</tt> parts that are left in the
message may be converted to <tt>text/plain</tt> if
<a href="?VARHELP=contentfilter/convert_html_to_plaintext"
>convert_html_to_plaintext</a> is enabled and the site is
configured to allow these conversions.
