The requirement of publishing to a topic and not to individuals could be a big limitation too. I'd love to use a service like this to handle all the one-off ema

The requirement of publishing to a topic and not to individuals could be a big limitation too. I'd love to use a service like this to handle all the one-off emails (billing receipt, individual notifications) within my web apps that only send to one person, and I want to use a 3rd party so I'm not supporting the email delivery side of things (keeping us out of spam boxes), but none of the email services around seem to offer what's needed for this, including Amazon SNS... From my experience, just setting up a secure email server with reverse DNS, SPF and DKIM, and having a privacy policy that you actually practice, is just not enough to ensure ongoing reliable delivery rates from your own server. Doing all that, we would still blast out email invites to ~50-100 people at a time, and one or two recipients would always find it in their spam box. Not good. With non-technical users, that became an annoying support problem and decreased the perception of our reliability/quality in their eyes too.