There is a script called "Foldup" which will mark duplicates for
deletion (as well as based on message age). It was originally a REXX
script (requiring you run OS/2), but I have converted it to PERL as
well (but never told anyone <G>), which will run on all platforms that
PERL runs on... which is all platforms. (-: However, it's not the most
userfriendly thing in the world.
the script is at http://www.vex.net/~x/files/foldup21.zip if you
want to try and figure it out.