You need to enable both Server’s home directory as well as Mail/FTP users.
With both these options enabled, you will be able to restore mail for the virtual server from the backup. You might also find the html, images and scripts of the website restored too, even if you may not want to restore them and you could simply delete them, but it is a Virtualmin quirk that only email cannot be restored.
my thought 1
I don’t think this is expected behaviour for the following reasons
Mail/FTP users and mail aliases has it’s own option tree and therefore should not be dependant on another option
I think Server's home directory and web pages should be renamed or retasked to public_html directory and web pages. This is because all/most user’s data goes in the home directory and this is required for any import (I know there are exceptions such as SSL certs, which I would prefer in the home directory but they have to be elsewhere for server protection from crashing)
My thought 2
or if I have got it a bit wrong then:
rename Server's home directory and web pages → User's home directory
rename Restore homes directory to restore 'public_html' directory
Move Mail/FTP users and mail aliases under User's home directory
When I get chance I will do a github issue for it (unless someone else want to help out ) , but the wording is not clear and you need to know about a quirk for mail only to be imported.
You need to enable both Server’s home directory as well as Mail/FTP users.
i think, Virtual server password ist the password from the owner, the first password you set on creating the virtual server.
Administration user´s password ist the password for users, like email or ftp user.