It takes a special kind to run and maintain a mail server. More so for doing it for such a long time.

It's behind a firewall. The only thing exposed to the outside is port 22 - and only pubkey login too.

And gee dude... It's been running for 18 years without being pwned 🙂

https://security-tracker.debian.org/tracker/

Depending on how it was configured it may or not be have been compromised. Probably better to go the nuclear option.

The amount of dos systems I have seen powering critical infrastructure in banks and hospitals is quite frankly nightmare fuel.

This is how massive botnets form

Everyone has a test environment. Some people also have production environments

Patience. It really helps to have all the latest set up: SPF, DKIM, DMARC. Then after that it's a matter of IP reputation, you can email the various blocklists and you wait for the rest of them to clear on their own.

I've had that IP for 10 years and it has never sent spam, and I've sent enough emails that people open that it actually does get through fine. I haven't had to think about it for a long time, it just keeps on working. Barely had to even adjust my Postfix config through the upgrades.

If you are worried that the NSA might be reading your email maybe it’ll be better for society if you don’t update … just saying.

Unfortunately that's not true. I've been running mail servers under my domain since around 2000, almost as long as Microsoft has been running Hotmail, and I was certainly following good standards like SPF and DKIM well before they considered such a thing... and yet Microsoft is the bane of my mail server's existence. Despite no compromises resulting in spam blasts, MS still regularly shuts me out with no reason given and no hits showing on their monitors. If I can find their email address to ask what the problem is, I get a generic "your domain has been cleared" sort of reply but never any reason why they blocked me in the first place.

I've started up new domains and never had an issue getting mail accepted.

There's a right way to do it, and most people that complain that hosting email is impossible don't know how to configure it correctly.

Eh, plenty of dos machines still used in banks and industry. It’s both scary and impressive. I have worked on cnc machines only a few years back that were from the 80s I think. The data transfer between the computer and the machine used a band of paper that had holes punched into it by a printer like device physically attached to the computer.