If you have your own domain, I recommend Migadu. They take care of all the boring parts of hosting email, while being cheap and very reliable. All you have to do is[1] follow their guude to setup some DNS records and double check everything is right. After that, you have a working email account with unlimited addresses, inboxes and a bunch more nice features.

[1]: Besides getting a domain name, which you should get anyway, since it gives you more control over your digital identity and makes it much easier to migrate providers in the future.

I use mailbox.org personally. Disroot is probably fine. Do they have 2FA? That would be the most essential thing you want here if you're worried about being hacked by an outside party. 2FA would even mitigate a password leak in most cases, since they'd only have 1 of the authentication factors.

If you're worried about hacking, you can do some things to mitigate the damage that would cause. Download important old emails and delete them from the server, this is pretty easy to do in a desktop client (like thunderbird or outlook) where you'd just move them to a local folder. That way if someone gains access, or they sell to someone that processes the data, they won't have the old emails (unless they for some reason retained a separate copy, which seems doubtful).

Sign your email up for https://haveibeenpwned.com/. Then you'll get notifications if there's any data leaks, including of your email provider. Obviously this is only useful if nobody has stolen your account before the leak is reported, but that's more likely than not (unless you're a particularly valuable target for some reason).

https://posteo.de or https://mailbox.org

Disroot should be fine for that. But what is the problem with Proton? Select protonmail.com and you should have no issues at all (proton.me is sometimes blocked because it is not a .com)

I've been using Fastmail for a few years and I'm quite happy with the service. Being a semi-large organization I expect their security to be OK, but if anyone has comments on that aspect I welcome them.

As for privacy, I always consider e-mail to be a postcard. If I want to encrypt something, I use GPG locally.

Posteo

I use also Murena Mail, apart of Proton https://murena.io Murena is a whole ecosystem, similar to GDrive, they even had launched the complete degoogled Murena smartphones

Tech Radar review

Murena’s key goal is to stop companies collecting unnecessary data from your phone and online footprints, which it says accounts for up to 12Mb every single day. Transparency is clearly important when browsing Murena’s website, which states that all of its servers are based in Europe including its Finnish email and cloud servers, resulting in full GDPR compliance.

Nextcloud, which sets the foundation for many of Murena’s services, is end-to-end encrypted, while a statement on Murena’s website reads:

“We don’t scan your data, we don’t log your app usage, we don’t sell your data, we don’t use ads in our online services.”

Negative points for some

• Only 1 GB Cloud for free (maybe enough if you only use the mail)
• Somewhat more expensive than others with the Premium plan

StartMail, Soverin, Disroot, Infomaniak Kmail, Mailfence, Mailbox.org, Kolab Now And Posteo

Gonna suggest a more lowkey one, https://runbox.com/

Will drop migadu into the pool of sugestions.

I believe cocks.li is still open, so you could use them. You said in another reply that you're not savvy enough for your own domain, but if you change your mind, purelymail.com With your own domain, you can easily switch providers without losing access to your addresses.

Purelymail.com

Checkout the list of recommendations published by the Free Software Foundation: https://www.fsf.org/resources/webmail-systems