Shown "MailBox Size" in Admin-Console 2014R2-HP1


just a question. If you click left on Users, in the right all users are shown with the informations in columns which you can configure and which can be exported to a csv file.
There is a column with "Actual Mailbox Size". How does this value get updated ?

I have had a User with more than 20GB shown in this view. After the user emptied a lot of folders and the trash, the value doesnt change.

I've done mailbox maintenances, but the value is still the same.

Any ideas ?