The problem starts here. Not many people who are not tech savvy even know what a custom domain is. Let alone having an email with a custom domain.
> You can't get banned from email
Ask people who get locked out of their gmail account.
What we techies miss is that there are more people who don't understand technology and are not willing to spend time learning about it as they have other more important things to do. Tech is just one of the tools they are using to get their tasks done. We cannot expect people to spend time understanding everything about tech. It is not surprising that it took a commercial company with aggressive behaviour when it comes to controlling users data to put BSD on regular non-tech consumer desktops. And why Microsoft Windows succeeded in being on regular consumers desktop OS whereas commercial Linux-based OS struggled; and the company that successful put Linux on mobile devices also has quite a record when it comes to users data.
We techies can talk a lot about decentralisation and owning data. But the regular non-tech users really don't care. They just want simple things done quickly using tech and get on with their lives.
Recently I saw videos from multiple news channels on how to use Mastodon. They were at pains to explain to users how there are multiple servers and one has to choose a server, which is run by individuals or organisations. And if the server goes down then the user has to move to another server. Regular non-tech users really don't want to get into this complexity. Has anyone ever seen TV channels explain with great effort how to use Twitter?