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When Exchange mailbox size quotas break

Sometimes an admin will set limits for a mailbox only to discover that Exchange is not enforcing them. The problem is rooted in a registry setting. Here's the fix.

Mailbox size limits are commonly used by Exchange administrators to keep Exchange database sizes from becoming unmanageably large. A good mailbox policy is especially important in Exchange Standard Edition, where there's a fairly stern 16 GB limit database size limit.

Sometimes, however, an administrator will set limits for a particular mailbox only to discover that Exchange is not enforcing them. This condition may persist until the system is rebooted or the Information Store is stopped and restarted -- neither option is practical for a production Exchange server!

The problem is rooted in a registry-controlled setting that was introduced in Exchange 2000 Service Pack 3 and is present in all editions of Exchange 2003. This setting governs how often Exchange rereads logon quotas -- i.e., mailbox size quotas -- for users. By default, it is set to two hours (7200 seconds) to prevent the system from rereading login quotas too often and possibly bogging down the system.

If users' mailbox quotas are changed often, however, you may want to increase the reread interval time, as polling the quotas once every two hours may not be often enough to properly reflect changes made. (Most computers running Exchange Server these days won't have any trouble handling the overhead generated by polling user mailbox quotas a little more often.)

To change the reread interval time for mailbox quotas, you need to edit the registry and navigate to the key:


Add a new DWORD value named Reread Logon Quotas Interval and set it to the interval in seconds you want to use. 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).

About the author: Serdar Yegulalp is editor of the Windows 2000 Power Users Newsletter and a regular contributor to

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