Well I'm looking to get my files off of Google, part of which is my emails. I have no problem storing them and whatnot, but one issue I've had when I hosted my own email before is some people decided to go and see what happens if they launched an attack on my mail server.
Thus, I'm looking for some sort of gateway provider, that'll serve as a "DDoS proxy" for email servers. I set my MX record to their server, they receive the email and send it directly to my backend server without ever storing it. I send emails through their SMTP gateway, they forward it straight out without storing it. It should also be able to handle DDoS attacks.
It should support DKIM and give me a dedicated IP for SMTP.