Bugfix.

functions/imap_mailbox.php

@@ -21,12 +21,14 @@ function isSpecialMailbox( $box ) {
            $move_to_trash, $move_to_sent, $save_as_draft,
            $delimiter, $folder_prefix;
 
-    $i = strpos( $sent_folder, $delimiter, strlen( $folder_prefix ) );
-
+    if ( $move_to_sent  ) {
+        $i = strpos( $sent_folder, $delimiter, strlen( $folder_prefix ) );
+    }
+     
     $ret = ( (strtolower($box) == 'inbox') ||
              ($box == $trash_folder &&
               $move_to_trash) ||
-             (substr( $sent_folder, 0, max( $i, strlen( $box ) ) ) == $box &&
+             ( substr( $sent_folder, 0, max( $i, strlen( $box ) ) ) == $box &&
               $move_to_sent) ||
              ($box == $draft_folder &&
               $save_as_draft) );