While attempting to fix a broken Postfix server due to a separate issue (https://www.virtualmin.com/node/37737) I tried to restore settings from a webmin backup, using Webmin > Webmin > Backup Configuration Files > Restore now and selecting "Network Configuration" and/or "Postfix Mail Server" under "Modules to restore".
Initially I selected Yes for "Just show what will be restored?" and a sensible-looking list of files was shown. But when I selected No for that option to do the real restore I got "0 files restored" every time I tried.
I was running it with root privileges so I doubt that file permissions or ownership were the problem. I'm also not sure if any of the listed files were actually restored despite the discouraging message - if they were it didn't solve my problem and I ended up restoring the entire server from a snapshot backup.
Unfortunately the Webmin Scheduled Backup screen (unusually) doesn't offer any way to date stamp or rotate the backups, so I only had a single backup file to try. Could that be a feature request as well please?