After a quick look into postfix.config and postfix.postinst, I'm not sure postfix/protocols is considered "changed" in case you preseed that value, in which case you'd skip the "setting inet_protocols" stage in postinst.
After a quick look into postfix.config and postfix.postinst, I'm not sure postfix/protocols is considered "changed" in case you preseed that value, in which case you'd skip the "setting inet_protocols" stage in postinst.