Personally, I have used nullmailer in the past to provide a sendmail compatible local install that immediately forwards email to the SMTP server of my choice. Has worked flawlessly.

Obviously, that doesn't come with HTML form support, but then I am also not sure I would like the same binary to handle both a HTTP(S) endpoint and email submission :)

At work I'm using Apprise (https://appriseit.com/) to deliver notifications.

Are you planning to add more services or to limit Posthorn to emails?

My current provider since almost two decades without any issues, except speed and storage limitations is all-inkl.com, but I really just use it for email and nothing else, therefore most likely overpriced at ~6€/month.

I would love to switch to some VPS/root or anything where I can SSH and install, compile my own services, but something where security is high and support is 24/7 available.

I do. Though I am self hosting it to have my personal email, being well... personal. Not for my company so maybe I am not the target.

Interesting project though. I always felt missing API to just send emails from some script in my mail server.

postfix/sendmail/dovecot/ingress setup

I am really happy with the setup. (So far)

We do, and thats why we use Postal [1].

The more SaaS applications that self-host email the better. It forces the big guys, ie Microsoft, to improve their blocklists and not lazily block entire ranges. Yes its work contacting them occasionally, but it keeps the internet open. The alternative is an internet where they control it all.

1. https://docs.postalserver.io/