It's not as bad as you think. Fastmail has a great import process. Transitioning to a new email address isn't really that bad. I did it about 15 years ago.

It's not as bad as you think. Fastmail has a great import process. Transitioning to a new email address isn't really that bad. I did it about 15 years ago. Whenever you log in to a site and you notice that it's using your old email address, you go into your profile settings and update it. After about a year you'll probably have hit 90% of your meaningful accounts.