You don’t have to have a single email address. I have plenty and various providers.

Then use mail client instead of webmail. I use thunderbird and have multiple boxes I just backup Thunderbird profiles folder to my NAS.

Local mail clients are excellent for taking full control of your mail without contortions.

Can you elaborate on what you mean by that?

I can say that in the article author was setting up own mail server and domain.

To have copy of all your mails locally or to back them up to NAS, having desktop mail client is much easier way than setting up mail server.