In theory it would be simple to provide a "cloudworkers cooperative" kind of service that just bundles the outbound mail so that traffic is sufficiently large to be whitelisted by the big providers. The two biggest problems are A. Scaling up sufficiently without attracting Spammers. Because even a single Spammer can ruin your reputation forever. So ideally you'd have a tight knit group of friends or similar. Even then you could hardly assure than no one ever gets hacked. B. Edge Cases. Even if your US or West European Traffic is sufficient to be whitelisted by all major Providers, how do you ensure that the occasional Email to a customer of an Indonesian ISP does not get blocked by their provider...