+Fix #599586 which was caused by duplicate boundaries. The fix is to
+simply use _addMixedPart from original Mail_Mime class which is recent
+enough in our case.
+
+--- roundcube/program/include/rcube_mail_mime.php~ 2009-05-01 19:58:12.000000000 +0200
++++ roundcube/program/include/rcube_mail_mime.php 2010-10-18 19:31:33.751930400 +0200
+@@ -102,12 +102,12 @@
+ * @return object The multipart/mixed mimePart object
+ * @access private
+ */
+- function &_addMixedPart()
++ /* function &_addMixedPart()
+ {
+ $params['content_type'] = $this->_headers['Content-Type'] ? $this->_headers['Content-Type'] : 'multipart/mixed';
+ $ret = new Mail_mimePart('', $params);
+ return $ret;
+- }
++ } */
+
+
+ /**