Founder of SellHack. Former Yahoo exec via Right Media acquisition. Startup marketer and biz dev since 2003. Startup mentor at FlashStarts. Built a few good companies and some not so good ones. Learned from all of them.
Agree with Lee's responses so I won't reiterate his points.
Additionally, the use of multiple domains is a strategy to ensure that deliverability for your transactional/product/account related messages isn't affected by any sales/marketing related email communications which may be sent through a different domain like a .co or a subdomain.
Gaming the system is temporary. Seems like you need to repair your IP/domain reputation and change your strategy for copywriting, send frequency etc.
ps - make sure you have DKIM and SPF records set up.