The idea seems great, apart from the anonimity and other features you are proposing, also the knowledge that your emails are "forever" on the blockchain and not dependant on the provider.
But before any money invested it would be great to see the MVP and gain trust that the devs can deliver.
To reach the MVP status is the hardest. It' like making the first million in business.
The Proemtheus concept is viable and received only positive comments.
Important is to make users understand that free-service is a trap where they trade the most valuable resource online: their profile and history.
About funding we must reach a balance: between an investor (concentrated power) and the blockchain model (decentralized / crowdsale).
This is just a delay, we are working towards delivering.