This is what i came up with:

#!/usr/local/bin/perl5 -w
use strict;

my $mbox=$ARGV[0] || die("Usage $0 <mailbox>\n");

open(MBOX, "<$mbox") || die("Can't open mailbox $mbox! ($!)\n");
my @mails = grep(/^From /, <MBOX>);
close(MBOX);
print @mails;
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