Hi, now it's bether.
But if you look at the release notes: https://www.smartertools.com/smartermail/release-notes/16
You will find that for Version 16.2.6439 (Aug 18, 2017) is stated "Hostnames are now required for domains. To simplify this, system administrators can use mail.%hostname% variable in Domain Defaults to propagate to existing domains. New domains will auto-fill the hostname's field with the domain's name, though the field is also editable."
So to me it's like an error in mentioned variable %hostname% that should be %domain%
I am right?