Earlier quoted context omitted.
In my book "email done right" is using email addresses on your own domain . Using @fastmail.com makes no sense to me. If being locked into somebody else's domain is acceptable, then Gmail is a better deal. And if you still insist on using somebody else's domain, then all bets are off after you stop using that account. First of all because the service provider can always change their policies. Just like how when Yahoo…
Using your own domain has the same problem. If you ever stop paying for that domain, or lose it for some other reason, someone else could purchase it and start impersonating your email.
If paying for it is a problem, then pay it in advance for 10 years and setup automatic renewal. Also leave a digital will. You probably want to do that anyway.