Not sure why someone would go through the pain of cobbling up a self hosted solution based on Postfix when you have fully integrated solutions like https://stalw.art/, which are a breeze to setup.
Also, people in the FOSS community tend to be wary of "open source" projects primarily developed by a commercial company under dual licensing.
My hope is that Stalwart will get to their webmail project over the next couple of years. I am on SnappyMail, but basically need to use desktop and mobile clients to get the full mail/CardDAV/CalDAV experience, which admittedly is already pretty awesome.
Currently, I have Stalwart, PostgreSQL, SnappyMail, and Caddy, all inside a docker-compose file, and I have migrated, moved servers, and all that no problem.
Stalwart is perfect for small self-hosters: a single binary, a single-directory resilient datastore (by default), a UI for every setting, and defaults that guide you to a DNS config which maximizes your sender score. Plus support for all of the "power user" features such as ManageSieve and shared CalDav folders.
Honestly, I love hosting my email now. And the last remaining battery which could possibly be included is now WIP: webmail!
Unix philosophy need not apply when there is exactly one use case for integrating these tools. (Or at least, one case which covers 99% of users. The remainder can keep their managerie of arcane config formats and susceptibility to unsafe language CVEs.)