When mailbox is over its quota, its StorageLimitStatus will be MailboxDisabled. If changing the quota, E2K7 & E2K10 is not enforced in 2 hours’ time, by default.
If need the change to take effect immediately, you have to dismount the DB or restart the Exchange IS service
The solution under http://serverfault.com/questions/294469/exchange-2010-mailboxdisabled-after-storage-quota-reached does not work based on the testing
Workaround is to change the 2 hours to 20 mins, let’s work on this approach http://n3ilb.wordpress.com/2011/05/19/user-mailbox-quota-limit-changes-may-take-up-to-2-hours-to-take-effect/
For a quick win, it is advised the user to housekeep its mailbox, and maybe disable & enable the cache mode