I would absolutely use an API for your transactional emails. I started out with our app sending the emails from our server and it was a constant headache. I now

I would absolutely use an API for your transactional emails. I started out with our app sending the emails from our server and it was a constant headache. I now use Postmark (http://postmarkapp.com/ http://postmarkapp.com/) and I have no problems. I believe Mailchimp also has an api for transactional emails not too. Sending emails this way is very inexpensive, especially compared to the headaches of managing it yourself.