efine Perl expressions to
selectively exclude messages during an
<a href="add.html">ADD</a> operation.  Unlike the
<a href="checknoarchive.html">CHECKNOARCHIVE</a> resource,
MSGEXCFILTER allows you to explicitly examine entire message headers
to determine which messages should be added.
</p>
<p>When defining the expressions, the raw message header will be in
the <b><tt>$_</tt></b> variable.  If the last evaluated expression
of MSGEXCFILTER returns a true value, or there is an explicit
<tt>return</tt> statem