I've been very happy using https://postmarkapp.com for several years now. It's not free, but it doesn't cost a lot at all. Mandrill was set up after I was already using Postmark, I was tempted to give it a go as I was already a MailChimp person, but didn't feel the need to switch in the end. I'm more confident that Postmark isn't going to close up shop anytime soon as they don't offer a free tier, just a trial.