If it's the privacy. then go with Protonmail. ProtonMail has some silly/marketing claim like "encryption" email which I think it just a marketing term. But they do has some nice encryption features intgrate nighly on their web app such as gpp and they are also maintain https://openpgpjs.org/
So I suggest to go with ProtonMail if you are more about privacy.
If you are more about vendor lock in, then you have to go with a provider that allow you to export data easiser. fastmail has JMAP for that.
On the side note, this is the reason I have been working on an email forwarding service[1] which has a REST API to export email out. You can literally `curl https://api.hanami.run/v1/mails` to get email in JSON format.
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Contrast that with Fastmail, Gmail, or other providers. At any moment someone who works there can look at customer emails. I prefer my emails encrypted at rest.
But at the $5/month level Fastmail appear to be much better value (30GB vs 5GB storage, support multiple custom domains vs single domain, 600 alias addresses vs only 5 at protonmail).
I also like what fastmail are doing with JMAP.
As they're both free for at least 30 days try them both out?
edit: fastmail also has good notes integration with iOS if that's of interest
I’m on Fastmail but will switch to Protonmail when my plan is due to renew. My emails are my life and it’s unsettling that people I don’t know can access them, and that they sit on a server unencrypted.
Unlimited domains and email ids. The limit is on the number of emails you send in a day.
One could compare that also to Megaupload (NZ) vs Rapidshare (CH) in the past…
It is not as if Swiss companies have a perfect track record of NOT working w/ three letter agencies based in the US[1].
[1] https://www.washingtonpost.com/graphics/2020/world/national-security/cia-crypto-encryption-machines-espionage/