All the tutorials are more or less outdated.

As DNS config, email should be easy config, this is the only problem I found in this service.

step by step should include (in this order):
1) DNS registries. Include multidomain
2) do we need to add users to the machine? If so, how to add them and the setup for folder/email permissions
3) required programs needed in order to set POP/IMAP (postfix, SSL...)
4) Test with email clients (settings ports, ssl) as thunderbird, outlook or gmail.
5) optional: webemailserver setup, in php and sendmail php function.

Maybe 1 click install of the LAMP with a kind of CPANEL for that should be perfect, cause is not user friendly at all.

Thanks