Home Diskspace (Quotas and limits) differs from server administrator - Where to look

Hello,

I run several Virtualmin VPS boxes without mail function. On of my clients complained that he receives mails that his server quota reached the limit of 5Gb. But when he looked at it there is a Home disk space of 3,23 Gb. But the server administrator is 5Gb.

So I changed the limit to 7,5Gb (see attachment) because I cannot detect what the difference is between those 2 parameters.

What does those 2 parameters mean to me and why is de server administrator far more higher than his used home space. I cannot detect where to look. There is no mailspace wasted, because it's outside the server.

Please help.