Technically, this is an RFE, but I think it is important enough that I am classifying it as a high priority bug.
Several of my end users have reached their quotas from being out over the holidays, etc. Currently, there is a system in Virtualmin for monitoring and notification of entire domain quotas, however there is no such system for end user quotas. But what's worse is that the user management table is deceiving, since it displays the "Mail file size" right next to the users "Disk quota", making it seem like that's all they have used of their quota. However, it apparently does not take other mailboxes into account besides the Inbox, nor does it take into account other files in their home directory. In other words, it is not reporting true quota usage.
So, for example, one of my users has a quota of 100 MB. Their mail file size only indicates 20 MB, so it looks like they are not in danger of reaching their quota. However, if I dig deeper and click on their username, I see that after their home directory setting, they have in fact used their entire quota and can no longer receive or access their mail.
So, in short, I think it is more important to display their entire quota usage, rather than only their mail file size, in the user management table. Also, there needs to be a way to notify users before they reach their quota and get cut off, similar to the way domain owners can be notified.