I don't think Mail::POP3Client does any such translation. It dumps to the file exactly what it receives from the server.

By the way, what's this crazyness?

        open(STDOUT, ">my_txt_output.txt");
        my $fh = new IO::Handle();
        $fh->fdopen( fileno( STDOUT ), "w" );
        $pop->HeadAndBodyToFile( $fh, $i );
        close STDOUT;
[download]

You should use

        open(my $fh, '>', 'my_txt_output.txt')
            or die("Can't create my_txt_output.txt: $!\n");
        $pop->HeadAndBodyToFile( $fh, $i );
[download]