U.S. users are leaving Facebook by the millions, Edison Research says

By far the biggest factor that had me stopping checking Facebook, and indeed LinkedIn, is number of utterly fictitious notifications they generate. There was a time a few years back when that red dot made me drop everything to check FB, but these days it’ll be some completely bullshit message they’ve made a notification out of. Feels like they got greedy for my attention and killed the golden goose there. I check it about once a day now, and in the browser not the app. If the notifications were still meaningful I’d probably still have the app and all the metadata that sent them.

Even more annoying is the same thing that they do with email notifications. They seem to keep inventing new "categories" of notifications all the time that I haven't yet opted out of - basically because I seem to be only able to opt out of just that specific category that they just sent me an email about, when I click on the "don't want to receive any more of these mails" link below the message.

And every time, they gladly acknowledge that I will not receive any more messages of that kind.

"Okay, you won't get any more mails about new messages from friends. Okay, you won't get any more mails about stuff your friends liked. Okay, you won't get any more mails about stuff some other random people liked. Okay, you won't get any more mails about new stuff posted in groups you joined. Okay, you won't get any more mails about new stuff posted in groups you did not join, but we think you might be interested in. Okay, you won't get any more mails about new photos posted by your friends. Okay, you won't get any more mails about new photos of cats posted on Facebook. Okay, you won't get any more mails about news articles with dogs in the title. Okay, you won't get any more mails about postings your friends liked that complain about the weather and were written by women of age 35-40."

Okay, admittedly the last three were exagerrated, but all the categories before have been actual "notification categories" that I successfully opted out of, before I put a generic Facebook email filter in my mailbox, because apparently nothing else is able to stop their overly-specific-category-generation-engine from spewing out new categories to keep me busy opting out of.

I’m not sure why this company is still allowed to send mail. Why can’t their mail servers be blacklisted?

There's nothing preventing you from setting up your own blacklist/filter. OTOH, most people don't care about this, and would be outraged if their mail provider started blocking facebook's mail.