Spam filtering on email is defederation. It’s just in the background and isn’t talked much about because it’s been automated quite a lot. But at the end of the day it’s still writing domain names into blacklist, essentially defederating from those domains.

No, that was pretty much how email worked for a long time. And IRC.

I remember someone even making a song "I am going to ban your domain" to the tune of "they're coming to take me away" to mock sysadmins who took this drastic measure too quickly.

Some university servers would block all email from abroad except for some whitelisted servers. My school blocked emails from another school because the students were badly policed and would just harrass other schools.

Some domains were universally blockdd because they were used by spammers and scammers.

This mostly softened into spam folders and increasingly sophisticated filtering, which is dominating today.

I think others are noting how it can be like this. In my experience:

• My kids' school accounts can only send emails to and receive emails from their teachers' email addresses. All other emails, including those from fellow students, are blocked.
• I frequently have issues with whitelisted email addresses at work. They sometimes are blocked and I have to go through the tedious whitelisting process all over again.

There are blacklisted email servers. And when email started you had loading circle for the whole internet.

Email has the same problems as federated lemmy servers.

Mail Servers can end up on distrubuted blacklists and unable to communicate with each other. When office 365 has an outage it causes huge problems because it's a single large provider having issues. That provider goes down but not email as a whole.

This is the same as what happened about a week ago when lemmy.ml and lemmy.world went down due to load.

I'm more seeing it as tiny villages in the same country. Sometimes there's a duplicate Starbucks over in the other village, but they might have a different daily special. And some villages have beef with eachother, and then you gotta sneak out if you still want to secretly visit your beloved in the other village. Or move over to your summer house in village #3, where you can both meet up without issues.

Smaller domains are blocked all the time, ask your local email admin.... just because you're not getting messages about it doesn't mean it doesn't happen

As someone who runs multiple email servers, this is exactly how it works.

Some email providers will randomly or purposely block emails I sent to them. I get arbitrary blocks or dropped emails on sent emails.

gmail and outlook and yahoo just silently drop my emails so I don't even get the courtesy of a notification, and it's almost impossible to get it appealed. The server issues will be fixed with time, reddit used to crash all the time.