After you configure the mailbox size restriction for a mailbox, that mailbox user can continue to send and receive messages that cause the mailbox to exceed the configured mailbox size.
For instance, a value of 1200 will cause Exchange Server to reread the quotas every 20 minutes.
It's not a good idea to set this to less than 10 minutes, however, as this may cause an excessive number of Active Directory lookups (which produce their own variety of overhead). Please let others know how useful this tip is via the rating scale below.
Restarting the Microsoft Exchange Information Store service causes the configured limits to take effect immediately.
This issue occurs because the Microsoft Exchange Information Store service uses the cached mailbox configuration to enforce mailbox size limits.
This may be a false notification, as it appears to a bug in Outlook 2010 when you’re running in Outlook Cached Mode.