--- a/.emacs-my	Tue Nov 08 10:04:08 2011 +0200
+++ b/.emacs-my	Tue Nov 08 10:13:15 2011 +0200
@@ -1232,6 +1232,10 @@
  gnus-check-bogus-newsgroups nil
  )
 
+;; If you're spooling in overlapping mbox folders, you probably want to delete
+;; all messages with duplicate message IDs.
+(setq nnmail-treat-duplicates 'delete)
+
 (setq
  gnus-posting-styles
  '(