Does anyone else send communications from sales orders, purchase orders etc from NetSuite to their customers and vendors through NetSuite? I have the situation where a clients users mailbox gets compromised and then we get bogus emails in out Netsuite account. Is there any email filtering software within Netsuite?

Yes, but have never seen spam originated from trx correspondence, only from Cases, which was difficult to stop. That was 2 years ago, maybe their spam filtering has improved (if they have one).