This causes Virtualmin functionality to break - particularly user quota for mailbox and perhaps even the ability of the owner of virtual servers to create users and mailboxes.
I would love it if Virtualmin would allow mailboxes to be stored in a non-default location. This has been discussed in the forum earlier too.
Note however, @ggnoredo , that Virtualmin does permit non-default location of /home so if you are willing to move not just mailbox files but also web content to another storage, then Virtualmin will work happily with that.
Thanks for suggestion! I tried to move folders but it didn’t work
I copied /homes folder to /mnt/VAULT/homes and tried to set home directory for each user within Webmin → Users and Groups page. After this it throws unable to create .usermin permission denied error on webmail or webmin page for all users. The folder is there. I checked permissions but they all same as before moving folders.