Understanding the Impact of Named Property and Replica Identifier Limits on Exchange Databases

Understanding the Impact of Named P...

Topic Last Modified: 2009-03-10

The Microsoft MAPI specification defines two types of properties: standard MAPI properties and named properties. All standard MAPI properties have fixed identifiers (IDs). The named properties provide a way for vendors to extend the standard MAPI property set by adding their own properties. Because the named properties do not have specific IDs assigned to them, MAPI provides a facility for dynamically creating unique IDs for named properties and maintaining a persistent mapping between the named property and its unique ID. However, the dynamic creation of these IDs means that the property IDs for named properties can vary from computer to computer.

The Microsoft Exchange Information Store service maintains a table of named properties for each database. When it processes a message with custom information, it automatically adds an entry to the named properties table for any custom property that has not been previously processed. For example, when a company implements a new application that integrates with Exchange and uses a specific Simple Mail Transfer Protocol (SMTP) X-header, the Microsoft Exchange Information Store service creates a named property for that custom information when it processes the first message that contains that information. Any subsequent messages that include the same SMTP X-header do not result in the creation of additional named properties.

Limits of Named Properties and Replica Identifiers

Exchange has a maximum limit of 32,767 property IDs for each database. If your Exchange organization processes an excessive amount of named properties, this limit may be reached over time. If this limit is reached for a specific database, Exchange is not able to create any new property IDs.

If this happens on a mailbox database, you must create a new mailbox database, move all the mailboxes to the new database, and delete the mailbox database that has reached the limit for property IDs. Then you may create a new mailbox database and move the mailboxes back to that mailbox database.

If the issue happens on a public folder database, the recovery process is more complicated. You must replicate all public folders to another server and delete the public folder database. You can then allow the content to be replicated back to the original server. However, if you already have replication configured for your public folders, it is likely that the other public folder databases in your organization also contain the items that used up the named properties and will also reach the configured limits. Recovering from this situation requires you to configure aging on your public folders so that older content that is not being accessed and might be consuming named properties is purged. Alternatively, you can also distribute the contents of the public folder database across multiple public folder databases. For detailed steps about recovering from the depletion of property IDs, see Events 9666, 9667, 9668, and 9669 Received When Named Properties or Replica Identifiers Are Depleted for An Exchange Database.

By default, Microsoft Exchange Server 2007 has a quota of 16,384 for named properties created by authenticated users and replica identifiers. The default quota for named properties created by users who are not authenticated is 8,192. These default quotas allow you to receive earlier notification about the potential depletion of property IDs. You can then take action before the maximum limit is reached rendering the database inoperable. Therefore, the quotas can help you minimize the effects of a malfunctioning application or a malicious denial of service attack. You can also configure the quotas for the number of named properties and replica identifiers. For detailed steps about configuring quotas, see How to Configure Named Properties and Replica Identifier Quotas for Exchange 2007 Databases.

For More Information

For more information about managing databases, see Managing Storage Groups and Databases.

To learn more about the security and protection features in Exchange 2007, see Security and Protection.