I built EmailEngine.
I've been building software around email protocols for a long time. This work has been mostly open-sourced and is well-known, like Nodemailer, the email client library for Node.js.
EmailEngine is a project I run entirely on my own. This includes software development, product planning, support, and so on. If you need help, you will get it directly from the person writing the code.
The open-source email projects I have built are used by companies like Microsoft, Apple, Mozilla, and Atlassian, to name a few. I put the same effort and care into EmailEngine as well.
EmailEngine is proudly built in Estonia.