Twitter is pretty abusive. And email used to be even worse.

It didn't get decent until it people started flocking toward centralized solutions like GMail, which (coincidentally or not) did a pretty decent job of reining in spam and viruses.

The industry got good at that, Google is not a magical spam filter in fact in some ways it is not even really that great at all.

There are many many ways to achieve the same or better results for spam protection they by using google

Such as? I switched to gmail mostly for the spam filtering.

It's federated but certainly not completely decentralized. Spam filters in a way have become "a protection (even if flawed)". With email, you can still send an email to anyone but if you send it from a personal server versus gmail, it's much less likely to be read.

* citation needed

That's not been my experience at all. I've been running my own email server for years and I've yet to hear about an email being blocked. I know many other people who run their own email server just fine.

Indeed, I've been successfully running my email server for the past five years and mail has no problem reaching gmail users.

I think people have just become defeatist.

I would argue Email is heavily abused, much more than Twitter. It's just not very noticeable if you have a good spam filter.