There are a lot of free developer-friendly mail services providing their APIs but what about a customers? You need also to easily create new mailboxes, send/receive emails, view analytics. Do you use own solution, any hosting or may be combining multiple services?
+1 for Mailgun - as @umuplus said, it's pretty easy to setup, free or cheap in most cases and is reliable.
I use it for side projects that send hundreds a month, to my day job that sends 1 million+ a month. Works fine for both.
I do track my emails (those that aren't just new user welcome email or password recovery) - I use my own in house built system for tracking, as well as systems I've built to send newsletters. For tracking I write to my own database as well as appending Google Analytics tracking codes.
Mario Giambanco
Director of User Experience Development
Umut Aydin
I use mailgun for my side project and a few customer projects. It's easy to integrate and free plan is more than I need. But I don't use it as an email marketing tool. So I don't care about tracking, replies, etc. All I can say is that it's perfect for sending emails for password recovery.