The main problem I find with these smaller email providers is the uncertainty of their future - they can easily disappear the next day, because they ran out of money or simply lost interest, and then you're f.cked. With Google, Yahoo! and Microsoft you can be at least sure they'll provide their email service as long as possible.
Which is exactly the reason that I have provided rather well-established examples.
Protonmail is developed by a group of people from MIT and CERN, and they raised more than half a million in their crowdfunding campaign [1]. They take the matter so seriously that its co-founder has talked about privacy at TED Global [2]. And riseup has been providing e-mail and VPN services for activists since around 1999.
Just check the links for more information.
The point is that if you take privacy and security really seriously, it is not very hard to find people just as serious as you.
As for riseup, they're always upfront and transparent about how their funding is going so that a case like that seems rather unrealistic for them (at least to happen suddenly)
