You can use something like this to create index: 

use strict;
use warnings;

use Mail::MboxParser;

my $mb = Mail::MboxParser->new( 'mbox', );

my $ind = $mb->make_index;
for ( 0 .. $mb->nmsgs - 1 ) {
    printf "%5.5d => %10.10d => %s\n", 
        $_, $mb->get_pos($_), $mb->get_message($_)->header->{subject};
}

[download]

In reply to Re^3: Mail::MboxParser pegs the CPU by zwon
in thread Mail::MboxParser pegs the CPU by oko1

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