You could help me
I searched the manuals and forum will, I see nothing in particular.
I want to configure postfix as using SMTP authentication, it asks me username and password that allows but never with the right information.
It also does not allow relays to other servers via SMTP, can allow only valid users on the server, which re-send an email to another server via email client like Outlook I get the error 554 relay not permitted
Some good and easy tutorial or Virtualmin can do, investigate and see no options relay, authentication and do not see how