EmailEngine comes from fifteen years of writing the email libraries other people build on.
It is a fair question to ask a one-person vendor, and the honest answer is not "trust me". It is that EmailEngine is built so that your business does not depend on my continued existence.
EmailEngine is self-hosted. There is no service of mine in the path of your email, nothing that stops working if my servers do, and no remote kill switch. An instance that is running today keeps running.
EmailEngine is source available. Your engineers can read it, audit it and build it themselves. If you ever needed to maintain it without me, you would not be starting from a black box.
A perpetual licence is a one-time purchase with no renewal to depend on. For teams shipping EmailEngine inside an on-premises product, that is usually the deciding factor.
An Estonian company, so the commercial relationship sits inside the EU. More to the point, EmailEngine runs on your infrastructure: your users' mail never reaches Postal Systems at all, so for that data it is neither controller nor processor. There is no sub-processor for your DPO to assess.
Every install activates its own 14-day trial from its own dashboard. No sign-up, no credit card, and no call with me required.