Focus on your app, not email
From the PostageApp blog:
After relaying millions of emails for our customers we are now taking the next step: PostageApp is now an end-to-end email delivery engine.
Not only can you offload the chore of sending email and making sure things deliver while monitoring the status, but now you can forget about maintaining an email server entirely and let the pigeon rocket do the work for you.
I’ve been using PostageApp for over a year in all of my projects. It takes less than a few minutes to get up and running and I never have to think about email again.