Applies to: Exchange Server 2010 SP3

Topic Last Modified: 2013-01-08

Microsoft uses the Messaging API (MAPI) to connect different messaging transport components. The MAPI specification presents most objects as properties. To identify these properties, MAPI uses identifiers, known as property identifiers or PropIDs.

Property identifiers are a set of hexadecimal values that range from 1 to 0xFFFF. This provides sufficient values for 65,534 properties. These properties are divided into the following groups, known as ranges:

The properties in these ranges are known as standard properties. Standard MAPI properties have fixed IDs, and represent all properties that are below 0x8000.

There is one additional range, which is the largest of the groups and which represents all properties that are at 0x8000 and above. The properties in this range are known as named properties. Named properties provide a way for vendors to extend the standard MAPI property set by adding their own properties.

Named properties fall into the following main categories:

Because named properties do not have specific IDs assigned to them, MAPI provides a facility to dynamically create unique IDs for named properties and to maintain a persistent mapping between a 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 mailbox. Messages that are sent over the Internet are transferred in a format that is known as Message/RFC822. This is a text format that includes messages in plain text together with headers that contain a set of key-and-value pairs. RFC822 includes support for a set of properties that are called X-headers. When the transport service processes a message that contains custom information, the transport service contacts the information store service to register named properties for X-headers.

Any subsequent messages that include the same X-header do not cause Exchange to register additional named properties.

Exchange stores these named properties together with the messages that contain the related X-header. Microsoft uses the extensible namespace PS_INTERNET_HEADERS to group the X-headers from messages that were received over the Internet.

Named Properties Limits

The following list summarizes some important points about named properties:

  • X-headers are fields in Message/RFC822 messages that hold certain important values.

  • Named properties is the method that Exchange uses to reserve an ID for a particular value.

  • After a named property has been allocated, it may not be deallocated. The property remains reserved for the particular name and GUID combination.

Because there are a fixed number of named properties available, Exchange uses a quota system to track the number of allocated named properties. In this system, the information store service warns you when available named property IDs are close to becoming exhausted. When a second threshold is reached, the information store service stops allocating named property IDs.

Named Property Exhaustion

Although many programs use named properties, Outlook uses the majority of them. When named property IDs are exhausted, Outlook cannot map a named property. In this scenario, you may experience symptoms that resemble the following:

  • Event IDs 9666 and 9667 are logged in the Application log. For more information, see Events 9666, 9667, 9668, and 9669 Received When Named Properties or Replica Identifiers Are Depleted for An Exchange Database.

  • Messages that contain properties that cannot be mapped are not delivered. When you examine the message tracking information for an affected message, the information resembles the following:

    550 5.2.0 STOREDRV.Deliver: The Microsoft Exchange Information Store service reported an error. The following information should help identify the cause of this error:

    MapiExceptionNamedPropsQuotaExceeded: 16.18969

  • When an add-in that adds named properties or X-headers to messages is installed in Outlook, certain messages may not be sent to other users in the organization. In this scenario, the sending user receives a non-delivery report (NDR) that resembles the following:

    The message reached the recipient's e-mail system, but delivery was refused. Attempt to resend the message. If it still fails, contact your system administrator.

To recover named properties in Microsoft Exchange Server 2010, use the New-MoveRequest cmdlet together with the DoNotPreserveMailboxSignature parameter. For more information, see New-MoveRequest.

Doing this depletes the named property IDs by retaining only named properties that exist on at least one message in the mailbox. If all named properties still exist on any message, none will be reclaimed.

Property Changes in Exchange 2010

Exchange Server 2010 includes improvements to address issues that may occur in Microsoft Exchange Server 2007. In Exchange 2010, named property resources are moved to the mailbox level instead of the database level. For more information about the property change issues that may occur in Exchange 2007, see Understanding the Impact of Named Property and Replica Identifier Limits on Exchange Databases.

For More Information

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