other external connections. The authenticated submissions you can then permit, while denying non-authenticated relay submission attempts. Differentiating between authenticated and non-authenticated connections is achieved using thesaslswitchchannelkeyword on your inbound SMTP channel, usually thetcp_localchannel...
This is like "In order to parse TCP, you need to parse the protocol that's wrapped inside TCP. So, if you want to parse TCP, you need to parse every protocol in existence like HTTP, XMPP, SMTP, IMAP, etc.". Saying that UTF-8 is too complicated is basically admitting defeat. If ...