use strict;
use warnings;
use Win32::OLE;
use Win32::OLE::Const 'Microsoft Outlook';

my $outlook = Win32::OLE->new('Outlook.Application') or die Win32::OLE->LastError;

my $namespace = $outlook->GetNamespace("MAPI");
my $folder = $namespace->GetDefaultFolder(olFolderInbox)  or die Win32::OLE->LastError; # <--- dead
my $items = $folder->Items;

print STDERR "Folder: ", $folder->Name, "\n";
print STDERR "Total entries: ",$items->Count, "\n";
__DATA__

The error message is something about "METHOD/PROPERTYGET getdefaultfolder"