When a user replies to a notification email, the mail sent to postmaster@[PMG-FQDN] gets forwarded to the administrator's email address.
In my case the PMG hostname is pmg.domain.tld, so the address is postmaster@pmg.domain.tld
I'd prefer to use some kind of noreply@domain.tld for the notifications or even better a way to modify the notification's from address using the ruleset.
This setting should be at least user-configurable in some way in my opinion...