Understanding Group Metrics

Applies to: Exchange Server 2010 SP3, Exchange Server 2010 SP2

Topic Last Modified: 2010-07-07

Group metrics is the collection of the following data about distribution groups and dynamic distribution groups in your organization:

Number of members
Number of members who are external to your organization

Group metrics data is used to support MailTips in Microsoft Exchange Server 2010. MailTips are informative messages displayed to senders while they're composing messages. For more information about MailTips, including a full list of MailTips available in Exchange 2010, see Understanding MailTips.

Group metrics data is used when deciding whether to display the following MailTips:

Large Audience This MailTip is displayed when a sender adds a distribution group whose membership count is considered a large audience as configured in your organization. By default, any message addressed to more than 25 recipients is considered a large audience.
External Recipients This MailTip is displayed when a sender adds a distribution group that has members who are external to your organization.

Determining these characteristics of distribution groups and dynamic distribution groups isn't a simple task. MailTips are evaluated every time a recipient is added to a message composed by a user. Calculating this information while senders compose messages isn't feasible because it would delay the display of MailTips, and it could have an adverse performance impact depending on the size of your organization.

To provide this valuable information to senders without an adverse performance impact, Exchange calculates group metrics data as a background process that can be scheduled to run during nonbusiness hours. When evaluating recipients for MailTips, Exchange reads the group metrics data.

Looking for management tasks related to MailTips? See Managing MailTips.

Group Metrics Generation and Distribution

By default, group metrics data is generated on the same Mailbox server that generates the offline address book (OAB). This is the case even if you explicitly disable group metrics generation on that server using the Set-MailboxServer cmdlet. The Mailbox server generates full group metrics data for all distribution groups and dynamic distribution groups every Sunday, and incremental updates for any groups that were modified since the last full generation. The day of the full group metrics data generation is fixed, but you can configure the time it's generated daily. By default, group metrics data is generated daily at a random time within two hours of midnight.

The following files are associated with group metrics:

GroupMetrics-<date>T<time>.bin This binary file is the main group metrics data file. It contains the membership and external members count for all distribution groups and dynamic distribution groups in your organization. The date and time sections of the file name are separated by hyphens. For example, a group metrics data file created on January 18, 2010 at 20:00 (8:00 P.M.) has the following file name: GroupMetrics-2010-01-18T20-00-00.bin.
GroupMetrics-<servername>.xml This XML file contains information about the Mailbox server configured to generate the group metrics data. This file is required by the Microsoft Exchange File Distribution service, and it points to the binary file that needs to be distributed.
ChangedGroups.txt This file contains the list of groups that were updated the last time group metrics data was generated.

Group metrics data won't be generated by default in the following scenarios:

You don't use OABs in your organization, or you use only public folders for OAB distribution.
The server responsible for OAB generation is a server running Microsoft Exchange Server 2007 with the Mailbox server role installed.

If any of these scenarios apply to you, you must configure an Exchange 2010 Mailbox server manually to start generating group metrics. For detailed steps, see Configure Group Metrics.

The group metrics data is distributed to the Client Access servers using the Microsoft Exchange File Distribution service. The Microsoft Exchange File Distribution service queries Active Directory for a list of Mailbox servers that have group metrics generation enabled, and then copies the group metrics data from the closest Mailbox server every eight hours.