Unknown mail not being returned to sender

[TonyGroves]

I'm using MDaemon 6.8.0.

I want to return all incoming mail for unknown recipients back to the sender, so in Primary Domain Configuration-> Unknown Mail, I have ticked "Route message back to sender", and unticked "Send message to the Postmaster user". However, MDaemon does the exact opposite of what I have specified, sending me (the Postmaster) notifications of all unknown-recipient mail, and sending nothing back to the sender. MDaemon has been restarted several times in the meantime, and the settings I specified are preserved.

Has anybody else come across this, and found a way around it?

Thanks.