You don't give much details, but I think this (from the Mime::tools documentation) could be of some help:

Here's some pretty basic code for parsing a MIME message,
and outputting its decoded components to a given directory:

use MIME::Parser;

### Create parser, and set some parsing options:
    my $parser = new MIME::Parser;
    $parser->output_under("$ENV{HOME}/mimemail");

### Parse input:
    $entity = $parser->parse(\*STDIN) or die "parse failed\n";

### Take a look at the top-level entity (and any parts it has):
    $entity->dump_skeleton;
[download]

You should use MIME::Tools. If it's because you didn't want to install it, a quick

perl -MCPAN -e "install MIME::Tools"
[download]

will do the job for you.

And remember, even for a one-time task you are better off reusing existing code. Some may say that doing otherwise is a form of "False Impatience" :-)

Guillaume