Have used both Zabbix and Prometheus for this. Highly recommend Prometheus over Zabbix if you can afford the time to learn it. It’s a bit weird at first but it’s so much easier to extend and manage then Zabbix in my experience.

You will need to set up Grafana to go along with Prometheus. But, again, it’s so flexible that you will end up being happier with it.

I also can’t recommend greylisting enough. If you haven’t already enabled it in postfix I strongly suggest doing so. It’s one of the easiest ways to reduce spam. By simply bouncing emails from new sources the first time and forcing them to retry, it cut my spam tremedously.

I have my mail server set up as a catch all so you can send to anything at my domain and it’ll land in my inbox. I use this to create usage specific addresses. If it’s something I know will produce spam, I just dev null anything going to that address. I can then also track where a spam source originated. For friends and family who email me regularly; they also know to append the current year to my email address, this allows me to rotate my email address every year.

I also run spam assassin and implement greylisting as well as blocking IP ranges from countries I know I’ll never receive legitimate mail from… it’s been an evolution.

100%. I’ve been running my own mail server for 10-15 years now and you’re spot on. I’ve wanted to migrate it to a more modern platform but I’m loath to relive the process of configuring postfix and dovecot. DKIM/SPF and Let’s Encrypt certs for IMAPS were also a bit of a headache to get sorted, and warming up the sending IP so gmail would stop sending me to spam… but once that’s all sorted it’s been very very hands off. I log in once in a blue moon to update it but otherwise it just sits and does it’s thing.