If you’re a heavy user of rules in Outlook, you may have hit Exchange 2003’s 32K quota limit. In Exchange 2007, the quota was increased to 64K as a default but can be changed to 256K.
To do this, open the Exchange Management Shell. To increase the quota for all users, enter the following:
get-mailbox | set-mailbox –rulesquota 256kb
To verify the setting for a mailbox, enter the following:
get-mailbox al | fl rulesquota
The response should indicate the quota for the user.
Thanks to Simon Page.