I have attempted to set up Postfix and Dovecot on my old VPS, but I think I made a mistake in the configuration.
When I want to repeat the process from the start, I tried to "apt remove" Postfix and Dovecot, but several old config files were not properly purged by "apt remove".
I ended up using broken configurations. I was burned out, then decided to skip it. Now I have a freshly installed server. I hope I do not make the same mistake.
