rename_timestamp_part_to_its_dateheader.pl

use DateTime;
use MIME::Parser;

my $dir = shift || Cwd::getcwd();
my $count = 0;

my @array = ();

touch_emls($dir);

sub touch_emls {
    my $dir = shift;
    opendir my $dh, $dir or die "$!";

    my $parser = MIME::Parser->new;
    $parser->output_dir( "/tmp" );
    $parser->tmp_to_core(1);

    for my $subf (grep !/^\.\.?/, readdir($dh)) {
        my $f = "$dir/$subf";
        if (-d $f) {
            touch_emls($f);
            next;
        }
        if (-f $f) {
            my $mail = $parser->parse_open($f);
            my $date_str = $mail->head->get("Date");
            my $epoch = str2time($date_str);
            $parser->filer->purge;
            utime $epoch, $epoch, $f; # touch file

            my $curdir = dirname $f;
            my $filename = basename $f;

            # 1475743648.M772840P29835.ip-172-31-10-24,S=5361,W=5456:2,
            if ($filename =~ m/^14[0-9]{8}\./) {
                my $org = $filename;
                $filename =~ s/^14[0-9]{8}/$epoch/;
                say "before $org";
                say "after  $filename";
                rename $f, "$curdir/$filename";
            }
            say $f . " => " . $epoch;
        }
    }
    closedir $dh;
}