MailTips Group Metrics and Large Audience Warnings in Outlook

In an Exchange Server environment, MailTips are the messages that are displayed to users while they are composing an email message in Outlook or Outlook on the Web. The idea behind MailTips is that they will alert the sender to potential issues with the email they are writing, allowing the sender to make an adjustment before they commit a potentially embarrassing error. Since MailTips warn about a variety of conditions, including Out of Office for recipients, and restricted distribution groups, they are quite useful.

In particular, the “large audience” warning is useful in reducing the likelihood that someone will send an inappropriate email to a large number of people. What you consider to be “large” might be different than what others do, but by default a large audience is 25 or more recipients. This threshold is defined in the Exchange organization config.

[PS] C:\>Get-OrganizationConfig | select mailtips*


MailTipsAllTipsEnabled                : True
MailTipsExternalRecipientsTipsEnabled : False
MailTipsGroupMetricsEnabled           : True
MailTipsLargeAudienceThreshold        : 25
MailTipsMailboxSourcedTipsEnabled     : True

If you address an email to 25 or more recipients, Outlook and Outlook on the Web will display a MailTip, such as the one shown in the example below.

You can also expect to see the large audience warning if the total number of recipients in all of the distribution groups you are sending an email to exceeds the large audience threshold.

The behavior of the large audience MailTip is slightly different though, if one single distribution group exceeds the threshold. Instead of seeing a warning about the total number of recipients, you’ll see a warning about the size of the large group.

It’s also possible that you’ll see no MailTip at all, even when a large audience has been included as recipients of the email. The reason is usually that the group metrics information for the groups has not yet been calculated. To save on resources, rather than calculate the group size on the fly, the group size is updated periodically and stored as an attribute on the Active Directory object named msExchGroupMemberCount.

If the msExchGroupMemberCount is 0, and you know the membership of the group is not 0, the issue is likely that the group metrics for that group are yet to be calculated. Group metrics generation happens automatically as an ongoing background process, but if your servers are overloaded then group metrics may not be updated regularly (or at all). Group metrics generation is performed by the arbitration mailbox that has the GMGen attribute set to $true.  You can find it by using the following PowerShell commands:

[PS] C:\>Get-Mailbox -Arbitration | Where {$_.PersistedCapabilities -match "GMGen"} | Select Name,Database

Name                                                        Database
----                                                        --------
SystemMailbox{bb558c35-97f1-4cb9-8ff7-d53741dc928c}         DB05

The mailbox server hosting the active copy of that database (DB05 in this example) will have some information in a file called ChangedGroups.txt to indicate the last result of group metrics generation. The file can be found in the GroupMetrics folder of the Exchange install directory.

Based on that information, if you find that your large audience MailTips aren’t working, the cause might be:

• Group metrics are disabled in the organization config
• The large audience threshold has been increased in the organization config
• The group contains external recipients, such as contacts (group metrics for external recipients is disabled in the organization config by default)
• Group metrics have not been generated for the group yet (you can check the group’s properties in ADSIEdit.msc)
• Group metrics are not being generated at all (check the ChangedGroups.txt file, check server performance)
• The group is a dynamic distribution group (group metrics work for DDGs, but some complex DDGs in my test lab never have group metrics calculated)
• Server-side or client-side cached data has not updated (test using Outlook on the Web to see whether it shows the same MailTips results as Outlook)
• Exchange Web Services is inaccessible or not working (another symptom of this is being unable to configure Out of Office settings)
• The user is on a mobile device or application (MailTips don’t work for mobile clients)