use Win32::OLE ('in');
use Win32::OLE::Const 'Microsoft Outlook';
use strict;


$Win32::OLE::Warn = 3;         # die on errors...

my $olLib = 'Outlook.Application';
my $OlApp = Win32::OLE->GetActiveObject($olLib) || Win32::OLE->new($olLib, sub {$_[0]->Quit;}) || die "$olLib: $!";  # get already active object

#    Get Message Folder
my $MsgFolder = $OlApp->GetNameSpace('MAPI')->GetDefaultFolder(olFolderInbox);

foreach my $Folder (in $MsgFolder->Folders) {
    ...
}