[Intermernet]

I ran multiple mail servers for years until about 10 years ago (moved out of the industry). The deliverability problem, as far as I know, hasn't really changed that much in the last decade. The key was to configure DKIM, SPF, only use secure protocols and monitor the various black/block-lists to make sure you aren't on them for very long. In my experience, if you end up on a few bad lists, and don't react quickly, the reputation of your domain goes down rapidly and it's harder to get off said lists.

You also want some spam filtering, which, these days, is apparently much more powerful with local LLMs. I used to just use various bayesian classification tools, but I've heard that the current state of affairs is better. Having said that, when you've trained the tool, it does a pretty good job.

It's not "plug-and-play", but it's not that hard. Once you've got it up and running the maintenance load goes to almost zero.

[Erwyn]

> It's not "plug-and-play", but it's not that hard. Once you've got it up and running the maintenance load goes to almost zero.

This is where I disagree. In my opinion it might not be that hard but the maintenance is really not zero as you just described how you need a reputable IP as a prerequisite and constant monitoring of block lists.

Just having DKIM, SPF and DMARC really was not enough last time I checked for getting delivered to let's say outlook.

[Intermernet]

I just realised, and this could be red herring, that almost all of the domains I've administered were based in Australia. I suppose it's possible that the IP ranges I'm dealing with have a better reputation than those from other countries. I have administered a few domains from US companies and IPs, but they've often been based in known data centres which may help their cause. I can't really talk to the reliability of hosting a mail server on a consumer / small business IP in the US / Europe/ Asia. It's possible that all known, common IPs in these areas have a natural disadvantage when it comes to reputation. I suppose try running a tunnel from your server to a small VPS in a knwon data centre? Not ideal, but it may help.

It would be annoying if entire US/European/Asian ISP IP ranges were immediately blocked. We should have moved on from that for many reasons unrelated to email.

[Intermernet]

The monitoring of block lists is much more important than people assume. I haven't looked into it in detail, but it always seemed like the reputation was based on a ratio of number of messages to known bad messages. If you have a moderately busy server, and you manage to keep off the block lists (or at least pro-actively remove yourself from them) then the reputaion gets higher and higher, and the maintenance goes down.

If you're a domain that only receives occasional messages, and you end up on Spamhaus and co, you're gonna have a problem. It seems that reputation at small scale is viral. You need actively good reputation and response time. But, honestly, it seemed that it didn't take more than about 3 months per domain I administered until they were just accepted by the net as valid, good actors.