Outlook Address Blocking and Spam Filtering

Why Outlook Address Blocking and Spam Filtering in General is not at all simple to explain, or get to work correctly

Warning: This is another of those topics that goes beyond strictly Outlook, simply because the issue(s) I'm about to discuss, while they interact closely with Outlook, are not necessarily influenced by Outlook or are under its control. And the way that Outlook interacts with the email servers is not precisely the same as how other email clients do. Everyone "does their own thing" to one extent or another.
For some years it seemed that. overall, the battle against spam was being won. And for some email service providers, Gmail and M365 being two examples, their spam filtering built on artificial intelligence is really, really, really good. You almost never have a spam message make it to your inbox or have a "real email" sent to spam for either of those services if you just let them both do their things and only do the very occasional "mark/unmark" as spam for a rare misdirected message. Sadly, they're the exceptions rather than the rule.

When you add in the fact that certain email service providers "take feedback" behind the scenes when you mark a message as spam or unmark a message incorrectly classified as spam, and use that to refine their filters, when you do that in your email client while others don't that's yet another layer of complication.

One member here recently mentioned that he's been trying to use Outlook's "block sender" function in an attempt to cut down on some traffic. This report triggered me to post about this on Technibble, a forum explicitly for those of us in the tech support business. I am getting more and more frustrated at how the "battle against spam" seems to be going in the opposite direction as it had been for some years. Some here might be interested in the topic and some of the revelations in it: Mark as Spam - Which email client(s) pass this information to which email service providers?

But, for those who don't want to read the topic, here are a couple of important takeaways (from the mouth of an Outlook and Microsoft 365 expert):
1. Outlook's mark as spam does nothing but train the local Outlook. If Outlook is attached to Exchange it will train that Exchange instance. None of this intelligence is used at the service provider level as far as I know.
2. Block sender functionality is actually dependent on Exchange too. So I'm not sure you can block sender without Exchange.
3. [In regard to spam filtering] That's because we've long since abandoned white lists and black lists and moved into active filtration. The system largely doesn't care what the user thinks, it's all keyword matching now.

My main point in posting here is to attempt to make it clear that the feedback loops between email clients and email service providers are both complex and inconsistent. When you add in the feedback loops between email service providers and email list providers (including, but not limited to, Groups.io) where if an email service provider's spam filtration marks a list/group message as spam you get unsubscribed (though ususally with a way to easily join again) things get even messier.

There are many layers and many players when it comes to spam filtering and exactly how it's going to work for you. It's very difficult to talk about this in any meaningfully specific way absent information about things like the email client in use, the email service provider, etc. It's not a simple, linear, step-by-step process.