Previously Jeff Garzik wrote:

You should add this to your procmailrc :)

# Nuke duplicate messages
:0 Wh: msgid.lock
| $FORMAIL -D 32768 msgid.cache

That has the nasty side-effect of spreading messages for a single
discussion amongst many different mailboxes depending on which path
happens to be the first to deliver an email to you.

Wichert.

-- 
Wichert Akkerman [off-list ref]    It is simple to make things.
http://www.wiggy.net/                   It is hard to make things simple.