Looks great! Do you have any plans to support third-party sending APIs (e.g. SES)? I see the reference to SMTP. I've been looking for a good solution for ad-hoc email campaigns (w/ templates) and for sending "systems" emails to an audience of customers . I currently look after lists on both MailChimp and EmailOctopus and get frustrated by the flat pricing for the size of the list and not how you engage with the list…
You can use SES's SMTP interface with listmonk. With some added effort, you can self-host an SMTP server and achieve better throughput, and depending on the volume, cost reduction. We've been running our own Postal SMTP instances successfully.
The issue is that you need to put lots of effort into getting off of blacklists, or your email won't be delivered.