There are a few related configuration settings that have appeared over some of the last several releases. They do not necessarily offer 100% of what's described above - but its at least a step in the right direction and certainly an incremental improvement over what we had previously.
Settings > Defaults > Domain defaults
"Use primary domain admin as postmaster address if there is no postmaster account"
Settings > General Settings > Server Info Tab
"Do not deliver postmaster messages at global level if handled at domain level"
Unfortunately as far as I can tell, neither feature is documented in the SmarterMail Online Help. I assume that's probably at least one of the reasons that this thread hasn't seen any official updates.
Many users would probably love to find out about these things someplace aside from the release notes, especially when a community member's forum post such as this has triggered a similar feature request.
It would also obviously be helpful if there was documentation in the expected location in the help file. This would allow SmarterMail admins to better understand the expected behavior of new configuration options.
I suggest that the SmarterMail community (users and staff) would likely benefit if there was a bit more follow-up and "closing of the loop" from SmarterMail when it comes to these type of forum posts. In this case the feature request is at least "partially underway" but nobody knows about it except for SmarterMail and those that discovered the checkboxes.
A little bit of communication really goes a long way.