If you're going to switch email providers to something like Fastmail, be smart about it and register a custom domain, and pay a little extra to hook it up to your new account (unless Fastmail lets you do it for free).
Just get a domain like `Smith.com` and then use the email `John@Smith.com`. Then it doesn't matter if you're using Gmail, Fastmail, Protonmail, etc. You can switch to a different company whenever you want (to get the best rate, avoid abusive terms, bad service, etc) without having to update your business cards, websites, online accounts, etc.
You'll still need to have a way to back up your old messages though.
I recommend everyone does this; not just if you switch to fastmail. Having your email identity tied to a particular service provider is a terrible idea. Email will probably be with us until we die; and chances are very high you won't want that particular email service provider for 60 consecutive years.
I used gmail with a custom domain for years before I finally decided to move to fastmail, which made the move pretty painless. That said, when I set it up gsuite with a custom domain was free. I don't think thats the case any more.
Just get a domain like `Smith.com` and then use the email `John@Smith.com`. Then it doesn't matter if you're using Gmail, Fastmail, Protonmail, etc. You can switch to a different company whenever you want (to get the best rate, avoid abusive terms, bad service, etc) without having to update your business cards, websites, online accounts, etc.
You'll still need to have a way to back up your old messages though.