Something

#!/usr/bin/perl -w
#
# Usage:        cat mailbox.txt | formail -s cpmsg.pl
#
#               where 'cpmsg.pl' is the name of this script
#
# Purpose:      Called by formail once for each mail message in a Berkeley-
#               format mailbox
#

$maildir = "$ARGV[0]";
if (!$maildir) { die("Usage: $0 $maildir"); }

# Formail increments this number for each message. The
# leading "0"'s must be removed (e.g. 001 becomes 1)

$filenum = ($ENV{FILENO} - 0) + 1;
$file = "$maildir/$filenum.";

open (OUTFILE,"> $file") or die("Could not open '$file' for write - $!");

while (<STDIN>) {
        chomp;

        print OUTFILE "$_\015\012";  # Add CRLF to each line!
}

close OUTFILE;