[carlosjobim]

The custom domain is all you need for complete e-mail sovereignty. As long as you have it, you can select between hundreds (thousands?) of providers, and take your business elsewhere at any time.

[sksksk]

You risk losing your historical emails if you don’t back them up somewhere

[carlosjobim]

Of course you use e-mail clients, so that you have your mails on at least one device. And separate backup as well.