The documentation is not great - I'd say it's just about barely enough to get an overall idea, but there's no one proper single definitive overview of what options exist, what are their possible values, what are the defaults, and how they relate to each other. Maddy docs, despite looking a bit sloppy, were a lot easier to get through. IMHO Stalwart makes it unnecessarily difficult to write a non-minimal static configuration file, hooking everything up correctly.
To be fair, maybe there is a page like that but I haven't found it, despite trying.
I know the Web UI allows to do the configuration by clicking through the forms, but this approach conflicts with declarative deployment practices. In my case it's giving me nondescript 500 errors in the UI with "Failed to write local configuration" in the logs because the .toml file is read-only.
But in general, I agree that it has not been a very smooth experience. Having messed around with maddy and mox, Stalwart has had quite a few gotchas. Despite being a single binary promising simplicity, I'm finding it to be a real challenge figuring out how it all fits together, and I'm mostly learning by trial and error since the documentation is often outdated.
My biggest gripe is that it doesn't use the config.toml for every setting, or at least doesn't seem to have the option to do so. I broke my installation and had to find the posgresql key-value pairs for the settings, which was made harder by the fact that everything was stored as binary, which also made me have to edit it as binary as well. These were very simple settings that would have been a breeze in a flat configuration file. I absolutely do not like how necessary the WebAdmin is to manage simple things.
That said, the integration with calendar/contacts is nice even without JMAP... Getting Thunderbird and Roundcube setup with plugins and proper settings made it so easy to get several users setup with calendars, contacts, and shared email-boxes and shared contacts right upon first login.
The S3 storage is also working great (Hetzner Frankfurt VPS paired with AWS eu-central-1), and AWS downtime a few days ago notwithstanding, I'm feeling good about the reliability that gives me, leaving me mainly with the PosgresQL data store the main thing to keep backed up.
This is a hugely ambitious software and as such, there will be many things that I will have a hard time getting used to as a hobbyist, but also a lot to be gained. I'm sticking around for now and waiting for version 1, improved documentation, and more clarity on how it all works.
Also, I only have 5 mailboxes right now holding less than 15GB of data total... S3 is still cheaper than the minimum at Hetzner since I don't need anything close to a TB.