The Internet is decentralised. There's Whatsapp, IG, WeChat, and more... But an outdated, insecure, but federated technology that everyone still uses: email. It's awesome tech - Gmail can talk to Outlook, and vice-versa? Revolutionary!
You should host your own at home too.
It used to be complicated to set one up - postfix, SMTP, dovecot, SpamAssassin, configuring, and maintaining them are quite daunting tasks. That's why mere mortals rely on giving up control to third-party "free email service" such as Gmail. You've heard about it - you're the product if you're not paying for it. Unfortunately, even if you pay for it, you are still giving control to these folks. What's stopping them from giving someone access to your account? And how would you even know about it? (even if it's illegal). And even if you know, would you care? Well, I don't know if you do - but I do.
You'll need a fresh Ubuntu installation for Mail-in-a-box because it's somewhat of an Ansible playbook for installing different packages needed to run a mail server. I personally prefer mailcow because each service are docker containerized, and you just need to run a single docker-compose up command.