Exchange 5.5 – Mailbox Limit Notifaction

Exchange 5.5 SP3 on Windows 2000 Sever.

Some of my users, scratch that, most of my users are not getting an notifaction that their mailboxes are over the size limit. Yes I have the limits set in the Private Information Store and yes each of their mailboxes has the “Use information store defaults” box checked. Any ideas?