Postfix on a stand-alone Internet host

Postfix should work out of the box without change on a stand-alone machine that has direct Internet access. At least, that is how Postfix installs when you download the Postfix source code via https://www.postfix.org/.

You can use the command "postconf -n" to find out what settings are overruled by your main.cf. Besides a few pathname settings, few parameters should be set on a stand-alone box, beyond what is covered in the BASIC_CONFIGURATION_README document:

/etc/postfix/
main.cf:
    # Optional: send mail as user@domainname instead of user@hostname.
    #
myorigin = $
mydomain

    # Optional: specify NAT/proxy external address.
    #
proxy_interfaces = 1.2.3.4

    # Don't relay mail from other hosts.
    
mynetworks_style = host
    
relay_domains =

See also the section " Postfix on hosts without a real Internet hostname" if this is applicable to your configuration.