You could ask Vincent http://clarity.fm/vincentroy if you have anything further to discuss.. but here's the short version.

We built custom code for all our trigger emails & notifications, and use www.sendgrid.com for SMTP API. We looked at others, but I'm friends with the founder at SendGrid and like them personally.

For free, you can use Google Mail api (if you send less then 500 messages per day I believe). It's simple / and gets great deliverability.

Hope that helps.

P.S. The emails I write, hence the personal feelings .. it actually comes from me.