add undocumented param

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@5849 d0543943-73ff-0310-b7d9-9358b9ac24b2

conf/voicemail.conf.xml

@@ -25,6 +25,7 @@
       <param name="save-file-key" value="2"/>
       <param name="delete-file-key" value="7"/>
       <param name="undelete-file-key" value="8"/>
+      <param name="email-key" value="4"/>
       <!--<param name="odbc-dsn" value="dsn:user:pass"/>-->
     </profile>
   </profiles>