I have been self-hosting my mail server for the past 5 or 6 years with success. Recently my ISP decided to close port 25 so I have to use a third party to deliver my outgoing mail.

I genuinely don’t understand what you are paying for. I must have missed something.

What cost?

It is hard to set up and you might need an SMTP relay since most ISPs close port 25. But it is feasible.

I have everything at home, including the mail server. The only third party to my setup is a SMTP relay. All on an Odroid H4+. With a backup server on a Raspberry Pi 4 at my daughter’s.

What I do is a local backup on a different disk with BorgBackup, then a copy of that local backup to a Pi at a friend’s place, with rsync.

Don’t you want to turn off the whole NAS? Of you don’t have the disks spinning, the NAS is probably useless.

Upgraded to Debian Trixie two days ago. Runs flawlessly

I use Watchtower just to notify me of the updates. So the docker socket is read-only.

I second that advice. When choosing the HDD, make sure it is NAS-grade.