Proprietary email platforms like Gmail and Outlook are common in use these days that most users aren't even familiar with open standards for email: IMAP, POP3 and SMTP. Popular platforms are based on these protocols, but don't expose them to the customer. Instead, the platforms act as one big wrapper service. For most customers, the concept of email stops here.
But the idea of email as a federated protocol goes further: it is to make communication possible between different users of different domains to communicate with each others, using the open standards mentioned above. This means, the email inbox is accessible in multiple ways, including using official apps or third-party apps, on the desktop, mobile, shell, or web-based user interface.
I have sampled about 30 family members but not one is familiar with the concept of owning a domain or purchasing an email hosting plan. Everyone has a @gmail or @yahoo address. Their understanding of accessing the email inbox is to visit gmail.com and yahoo.com, or use their mobile apps. These for-profit platforms are selling convenience.
Case in point
I share my email hosting plan with a family member whom I recently encouraged to own a domain. We had to change the mailbox password because they were worried it may be exposed. Changing the password on my hosting admin panel is straightforward but the larger challenge was in helping them navigate their K-9 Mail settings on Android to update the password. Eventually they came home to sort this out, but it'd have been nicer if they could do it on their own. One idea that we spoke about is that, I can update the new password on their Bitwarden vault, which they can later auto-fill on K-9 Mail.
I wish we can turn this around one day though: by focusing on educating users of the advantages of owning their data, and on how to navigate these open standards and apps.