https://www.privacyguides.org/en/email/

Normal email is unencrypted when it's on the wire in transit. (Nowadays they use SSL between servers, but it's totally readable by every server in your pathway. Which isn't much better ). The best you can hope for email is to encrypt it and store it at rest once it arrives at the server. If you self host the server you could have one way encryption enabled. If you don't want to self host the privacy guide options are pretty good.

Don't have any conversations via email if you can avoid it. Prefer end-to-end encrypted platforms like signal instead

I own a custom domain and actually use Tutanota as my host. Self hosting is a nightmare and easy to fuck up, which leads to your emails getting sent to spam or just not receiving. I use custom domain support in Tutanota that costs me $12/yr (2 custom domains) and my domain is $15/yr. Since custom domains stick out like a sore thumb, if I need privacy then I will use AnonAddy to forward to my email with an anonymous forwarder.

Like 99.9% of my emails aren't encrypted but that's not the point. Tutanota removes a lot of the privacy leaks via metadata and has privacy protection measures by default like disabling images from automatically loading. Also it's calendar/contacts/email all rolled into one and everything is e2ee. Not to mention, unlike ProtonMail, they have their own push service that works on DeGoogled Android and can be installed from fdroid.

I use fastmail.com to generate e-mail aliases. Creation is rate limited, but they are virtually unlimited; I have 500+ and counting. Aliases are randomly generated as wordone.wordtwo1234@fastmail.com, so they aren't identifiable to your account.

If you want to self host, I recommend mailcow. It is not that hard to install and if you follow the instructions you'll have a working solution whose mails are not considered spam by every other sane server. Sadly, some operate with whitelists.

Anonaddy/Addy.io to create aliases, then PGP encrypt it before forwarding to my Google mailbox.

I also use Proton but considering ditching it in favor of Anonaddy.

People here seem to think that email alias providers are more secure then a custom domain. I would argue they are the same.

If someone is going through the trouble to find you, the alias provider will give up your payment information and your real email address.

A custom domain will give up your registered information.

If you want a truly anonymous email, don't have it funnel to your personal / main account.

self host. Don't trust random "privacy" companies

Do not use proton, get yourself a domain and then use something like Migadu to host it for you on that domain. Then you can also use anonaddy to add anonymous addresses where needed.

Tutanota with own catch all domain

I'm using Skiff Mail with two custom domains.