I've started recommending my clients Postmark after trying a lot of email providers. Postmark is a small company yet one of the best in the transactional email world! The setup process, stats for emails and user interface are minimal yet do a great job. It has plugins for WordPress which uses API to send emails rather than SMTP connections. This is a better way to send emails because, SMTP uses a synchronous connection and REST API is an Async. This way they are able to deliver super fast email service. Most of the transactional emails like order information, login details, contact us messages and most day to day messages go through the postmark service. They also offers credits for bootstrapped start-ups. Review collected by and hosted on G2.com.
Customer support is great but not the best! They take time to respond like 24 hours or so. I wish they had a 24 hours service. Also pricing is a bit premium but well worth the price and the smooth service they offer. Review collected by and hosted on G2.com.