Wikipedia:

Fastmail is a subscription-based[2] email hosting company based in Melbourne, Australia.

So the rant I'd written about US companies handing over data regardless of location has been chopped.

For those that didn't read it, a backup still remains in the US for now, as they only have 1 data centre in Europe at the moment, so not complete data sovereignty yet.

Most of the solutions I've looked at utilize Roundcube in some form or another. It looks like exposing Roundcube to the internet is a really bad idea. I guess I'll need to restrict Roundcube to VPN-only or something like that.

https://cyberinsider.com/data-breach-at-cock-li-email-service-exposed-over-1-million-user-records/

I'm just first looking at all of this. There appear to be many security considerations, and when I finally do pull the trigger, its gonna break my existing ImprovMX email forwarding, so I'm in no rush. When I'm done, I want email and nextcloud running on the same server, pretty much forever, so I want it done right the first time.

I'm honestly not sure what the term swarm means but it could be? AFAIK this all runs off of a single docker compose file. You do "docker run <compose.yml>" and it will automatically download and run all the containers as needed. This is very similar how their upgrade script works when you want to update everything.

I'm still figuring out my email. I'm definitely gonna run my own mailserver.
I was going to do mail-in-a-box because it comes with the nextcloud feature installed, but it requires a specific version of ubuntu, which is kinda weird.

I guess its going to be mailcow. https://docs.mailcow.email/
I have some degree of experience with docker, but I'm probably going to learn things in the process of getting it all built.
I've read about it some. Whole bunch of containers. Is this a docker swarm?
I'll get docker setup. I guess I need git too.

Hmm. Ya I getcha about the SMTP problems.
I have a couple ways around that, but I'll do my best to join the system as a full domain w/smtp. I can fall back to using my work smtp if I have to.
Thanks, friend!

I've not heard of mail in a box but I'm using Mailcow myself. They have a full docker compose and update script that will tear down and upgrade the stack itself. Been using it for years with little issue.

It's a good thing you have a mail forwarded already as you risk getting immediately grey listed without one for outgoing mail. I'm using SMTP2Go myself and it works great. They have a free tier that works for very little volume outbound. I may need to see about moving to ImprovMX if it makes sense to do so.

My use case is basically for internal system alerts and testing for work mainly. I don't want to rely too heavily on my internal mail server because if it blows up for some reason, I don't want to have important information in it that could be costly (time consuming) to recover.