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https://purelymail.com/ I haven't try it yet, but it is only 10$ per year

$10/y seems ridiculously cheap. Too cheap. I'd be worried they may go out of business.

I'm a very happy migadu.com user. Set fee for unlimited storage and unlimited addresses. Very simple but effective admin UI too.

Mailbox.org

I’m a happy user and never touch the web app. It works, but a dedicated mail client is a superior experience.