Free email for all, if I understand this correctly. The goal is to make it easy to set up new Delta Chat accounts.

"You may peek at nine.testrun.org, and after installation of a Delta Chat app, simply tap or scan the below QR code to get a @nine.testrun.org address"
https://delta.chat/en/2023-12-13-chatmail

And you set up such a site yourself. Email-in-a-box:
"This repository helps to setup a ready-to-use chatmail server comprised of a minimal setup of the battle-tested postfix smtp and dovecot imap services."
https://github.com/deltachat/chatmail

Although to be honest, I was unable to figure out how they control the remote. I see that the deployment script needs root access to the server, but I haven't seen any distro-specific installation scripts so I guess they assume it's all there? And if so, does that mean I can run it for my own server? But if I use Apache and they talk about nginx, some stuff is bound not to work… Interesting nonetheless!