Does anyone know what I would need to do to loop through each item under inbox?

Sure. Determine what $d looks like and then walk that data structure.

use Data::Dump::Streamer;
my $xml = XML::Simple->new();
my $d = $xml->XMLin("sample.xml",ForceArray => 1, KeepRoot => 1);
Dump $d;
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Gives

$HASH1 = { 
  inbox => [ 
    { 
      item => [
        {
          description => [ 'Bar' ],
          title       => [ 'Foo' ]
        },
        {
          description => [ 'Foobar' ],
          title       => [ 'Baz' ]
        }
      ] 
    } 
  ] 
};
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Now, for that sample XML it seems to have lots of redundant hashes and arrays if what you care about are the items. So, maybe don't use the extra options:

my $d = $xml->XMLin("sample.xml");
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Gives:

$HASH1 = { 
  item => [
    {
      description => 'Bar',
      title       => 'Foo'
    },
    {
      description => 'Foobar',
      title       => 'Baz'
    }
  ] 
};
[download]

So with that, $d->{item} would appear to be an AOH. Loop through it like this:

for my $item ( @{ $d->{item} } ) {
  print "$item->{title}\n";          # for example
}
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