AWS and Digital Ocean basically beat them. Mailgun is awesome though. Love using it. I see rackspace as being a perfectly wonderful private company that makes good money but they don't have enough glitz to really make it as a publicly traded company. Not enough product innovation or new markets or anything like that.
We've been using Rackspace and haven't evaluated Mailgun yet. Can you help us with a quick comparison based on your experience?
Mailgun is a transactional email service that is basically free unless you are doing huge volume. The api sets the standard for documentation. If you need more features with your transactional emails you can sign up for Sendwithus.