use strict;
use Win32::OLE qw(in with);
use Win32::OLE::Const 'Microsoft Outlook';
$|++;
$Win32::OLE::Warn = 3; # Die on errors

my $OL = Win32::OLE->GetActiveObject('Outlook.Application')
        || Win32::OLE->new('Outlook.Application', 'Quit');

my $NameSpace = $OL->GetNameSpace("MAPI");

my $Contacts = $NameSpace->Folders("Public Folders")->Folders("All Public Folders")->Folders("Test");


my $contact_items = $NameSpace->Folders("Public Folders")->Folders("All Public Folders")->Folders("Test")->{Items};
my $it = $contact_items->GetFirst;  #get the first item
foreach my $item (in $Contacts->{Items}){
  $it->{Categories} = "New Categories Value";
  ## Code needed here to save the above new value?
  $it = $contact_items->GetNext;
}