diff --git a/grokmirror/pi-piper.py b/grokmirror/pi_piper.py
similarity index 100%
rename from grokmirror/pi-piper.py
rename to grokmirror/pi_piper.py
diff --git a/man/grok-pi-piper.1 b/man/grok-pi-piper.1
index d1f3da6..01c408b 100644
--- a/man/grok-pi-piper.1
+++ b/man/grok-pi-piper.1
@@ -51,12 +51,17 @@
 \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
 [DEFAULT]
 pipe = /usr/bin/procmail
+# Prune successfully processed messages
 shallow = yes
 
 ~/.procmailrc
 \-\-\-\-\-\-\-\-\-\-\-\-\-
 DEFAULT=$HOME/Maildir/
 
+# Don\(aqt deliver cross\-posted duplicates
+:0 Wh: .msgid.lock
+| formail \-D 8192 .msgid.cache
+
 ~/.config/lore.conf
 \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
 [core]
diff --git a/man/grok-pi-piper.1.rst b/man/grok-pi-piper.1.rst
index 18d16bb..1c14b5e 100644
--- a/man/grok-pi-piper.1.rst
+++ b/man/grok-pi-piper.1.rst
@@ -26,11 +26,16 @@
     -----------------------
     [DEFAULT]
     pipe = /usr/bin/procmail
+    # Prune successfully processed messages
     shallow = yes
 
     ~/.procmailrc
     -------------
     DEFAULT=$HOME/Maildir/
+    
+    # Don't deliver cross-posted duplicates
+    :0 Wh: .msgid.lock
+    | formail -D 8192 .msgid.cache
 
     ~/.config/lore.conf
     -------------------
diff --git a/setup.py b/setup.py
index 1aabf48..86a0571 100644
--- a/setup.py
+++ b/setup.py
@@ -64,7 +64,7 @@
             "grok-fsck=grokmirror.fsck:command",
             "grok-manifest=grokmirror.manifest:command",
             "grok-bundle=grokmirror.bundle:command",
-            "grok-pi-piper=grokmirror.pi-piper:command",
+            "grok-pi-piper=grokmirror.pi_piper:command",
         ]
     }
 )