$VAR1 = {
          'outdoor' => {
                         'cat' => 'other',
                         'desc' => 'Outdoor activities'
                       },
          'Testlist' => {
                          'cat' => 'other',
                          'desc' => ''
                        },
}

##</code><code>##

for my $list ( keys %lists ) {
    $lists{$list}{desc} = check_desc $lists{$list}{desc};
    $list = "[mailto:$list\@example.com $list]";
}