There’s no way to rebuild them, as there’s no way to determine what is correct
The “BOUNCE” thing you’re seeing can happen if the address is setup as an Alias in the Virtual Server, and in “Edit Mail Aliases”, and address is setup with the “Bounce mail?” checkbox checked.
Otherwise, perhaps if you have a test system setup, you could pull those files from there.
For example, if you install something like VMware Server on your desktop (which is free), you can install your distro in a VM, and after installing Virtualmin, pull the config files from it.
That sounds remarkably similar to the error you had been getting – did you by chance verify that you don’t have an alias setup for this particular user that’s causing it to bounce?
Look in “Edit Mail Aliases”, and make sure you don’t have an alias with “Bounce Mail” checked.
I had “Bounce Mail” for all Aliases activated. Crap.
I didn’t notice that type of Alias, because it was a failure for a Subdomain.
I imported the whole Virtual Server from a Plesk System. The Alias must have been created by that Import.
Maybe this should be checked by the people at Virtualmin, cause its very annoying!