This might come a bit late, but I'm surprised you haven't heard about services that send transactional emails for you. Their track record spamwise is usually quite good, but usually does require some configuration on your part( get DNS records right, etc...)
I think the services take the guesswork out of sending email reliably, but the fact remains that the one of the most important factors is how you created your list, just before having an easy unsubscribe link , something that these services sometimes take care of (for email lists, newsletters) or sometimes don't (transactional emails, sent to say one of your users when registering on your site).
Some of the best known companies that provide this service are sendgrid, postmarkapp and mailjet
Here is a comparison of most email-as-a-service providers
Disclaimer: I am consulting for mailjet as a developer