What you get with mailbox.org that you don't get with ProtonMail:
* IMAP and SMTP
* Support for hardware 2FA dongles like Yubikey
* Ability to use your own GPG keys
* Very capable mail filter config tool
* Calendaring and contacts (with nice URLs so it's easy to use on Android via DAVdroid instead of Google's stuff)
* File storage
* Web-based spreadsheet, word processor and presentation tool
Their jurisdiction is Germany so you get whatever is left of EU privacy laws plus the Germany-specific ones.(Also who runs privacytools.io? Is he/she reputable?)
Here is an extract from Fastmail TOS:
Fastmail can disclose your info/data if it thinks it's in the interest of the company: "The Service Provider will not monitor, edit, or disclose any personal information about you [...] unless required or allowed by law, or where the Service Provider has a good faith belief that such action is necessary to: [...] (2) protect and defend the rights or property of the Service Provider; [...] (4) act to protect the interests of its members or others [...]
- Fastmail can immediately cancel your account for any reason: "The Service Provider may terminate your access to any part or all of the Service and any related service(s) at any time, with or without cause, with or without notice, effective immediately, for any reason whatsoever, with or without providing any refund of any payments."
- Fastmail can disclose your info/data if it thinks it's in the interest of the company: "The Service Provider will not monitor, edit, or disclose any personal information about you [...] unless required or allowed by law, or where the Service Provider has a good faith belief that such action is necessary to: [...] (2) protect and defend the rights or property of the Service Provider; [...] (4) act to protect the interests of its members or others [...]
By comparison, mailbox.org TOS are much better.
Also mailbox.org offers GPG encryption, which Fastmail doesn't (AFAIK).