The AD attribute mdbOverhardquotalimit is a property of the Exchange store schema which reports the the maximum mailbox size,
in kilobyte (KB), over which sending and receiving mail is disabled. A NULL value for mdbOverhardquotalimit means that there are no limits
for that particular mailbox. A value of zero '0' means tthat mailbox cannot send or receive any mail.
The MessageStats report 'Mailbox Quotas' (under MessageStats Reports | Mailboxes | Sizes and Quotas) reports the value of mdbOverhardquotalimit
but it is labeled as 'Receive Quota (KB)'. When the value of mdbOverhardquotalimit is NULL it is reported as a zero '0' in this report. This is misleading
because when the value of mdbOverhardquotalimit is actually zero '0' it is also reported as a zero '0' in this report, and there is no way to tell if a particular
mailbox has no limits or if it cannot send or receive mail at all.
Enhancement request TFS54346 has been submitted to Development for consideration in a future release of MessageStats.