Email has "instances" that act as gatekeepers. Gmail is one, Outlook is another, Fastmail is...
They are both federated systems and on these systems (email, fediverse, matrix, xmpp...) end users have accounts on servers that then connect between themselves to create the whole network.
The only difference is the underlying protocol and/or the main purpose.
I think we need to treat social networking as part of messaging
Some mail providers require you to contact them to get on an allowlist to even be able to deliver email at all. Others do not formally require that, but you may have to enroll in a postmaster programme in order to track your deliverability. Yet others there's no hope at all, except running after the most recent fad in spam fighting (like DKIM/DMARC/SPF etc.), only to find that even fully and correctly configured DKIM (which I don't like on my private email for many reasons) is by far no guarantee for not getting your email marked as spam (and thus, on some providers, hidden by default), even from IPs and domains which have had no spam emitted from them for many years.
So... Yeah. It's not heard of in the public media because those affected most by this don't have any leverage. The big mail service providers (MSPs) presumably have their agreements among one another to protect their business, but if you're just doing friends&family, good luck getting anything except an autoresponder when you run into troubles.
(To offset some of the criticism here, I have had very positive experiences with contacting postmasters of some large German email providers when issues happened, so there's that.)