I am trying to protect my local network from spam with the help of "rspamd"+"postfix" services.
I almost made it :)
1. postfix receives messages
2. rspamd filters messages
3. postfix is NOT delivering messages to the target mail server - I'm stuck here.
Of course, I have set up a domain list. I also tried to set up Smart Host but to no avail.
Domains is correct to deliver inbound mail to its destination. Smarthost is for outbound mail. You might want to look at the logfile, why it does not deliver inbound mail.
There's two good books about postfix, but that's possibly a bit much in the OPNsense context.