How to Use Exchange Dynamic Distribution Lists to Address Specific Mailboxes

Send Email to Filtered Sets of Recipients

After explaining how to use a custom attribute to store users’ beverage of choice and surface that information in Office 365 apps through the Microsoft 365 profile card, the question came up if it is possible to create a dynamic distribution list using the same custom attribute. The answer is “absolutely!”

Dynamic distribution lists are a very powerful way of addressing specific sets of mail-enabled recipients. Table 1 compares their capabilities against those of dynamic Microsoft 365 groups.

Dynamic distribution listsDynamic Microsoft 365 groups
LicensingIncluded in Exchange OnlineNeed Azure AD Premium P1
FiltersResolved against Exchange Directory StoreResolved against Azure AD
Can includeAny Exchange recipient type (mailboxes, public folders, mail contacts, etc.)Azure AD accounts (including guests accounts and hybrid users)
UseAddress emailDetermine membership of a group used to manage access to group resources. Can also be used to address email.
Table 1: Comparing Dynamic distribution lists and dynamic Microsoft 365 groups

Some on-premises Exchange organizations use thousands of dynamic distribution groups. Because of the presence of other methods to address sets of users like Microsoft 365 Groups and Teams in Office 365, dynamic distribution lists are not as heavily used. But as we’ll see, these lists are easily to create and use.

Filters Against the Directory

The core of both types of dynamic groups is the filter used to find objects in the source directory. The filters can be very complex when multiple attributes are involved, but in this case the filter needed to find users with a particular value in a custom attribute is straightforward. For example, to create a dynamic distribution list of mailboxes whose owners like beer, we can either use the Exchange admin center or run the New-DynamicDistributionGroup cmdlet:

New-DynamicDistributionGroup -Name DynamicBeer -DisplayName "Dynamic Beer Drinkers" -ConditionalCustomAttribute9 Beer -IncludedRecipients MailboxUsers -PrimarySmtpAddress -Alias Beer.Drinkers

In this case, because we decided to use CustomAttribute9 to hold the drink preference, we can use what’s called a “precanned” filter. In other words, Exchange knows that custom attributes are often used for filters, so the cmdlet supports an easy way to include these attributes in filters. The ConditionalCustomAttribute9 parameter is set to “Beer” and the IncludedRecipients parameter is set to MailboxUsers. Together, this creates a filter to find any user mailbox whose CustomAttribute9 is “Beer.”

To complete the setup of the new dynamic distribution list, we use Set-DynamicDistributionGroup to define who is the list owner and create a mail tip to give an indication to users about the list’s purpose:

Set-DynamicDistributionGroup -Identity Beer.Drinkers -ManagedBy -MailTip "Mailbox users who like beer"

Some judicious cut and pasting will quickly generate a set of dynamic distribution lists for people who like water, wine, cola, and so on.

Testing Recipient Filters

If you want to be sure that the filter created for a dynamic distribution list will locate the correct mailboxes, you can run the Get-Recipient cmdlet and input the recipient filter for the list. Here’s how:

Get-Recipient -RecipientPreviewFilter (Get-DynamicDistributionGroup -Identity Beer.Drinkers).RecipientFilter | Select DisplayName

Kim Akers
Imran Khan
James Ryan

To have more mailboxes picked up by the filter, update their CustomAttribute9 with the value used by the filter. For example:

Set-Mailbox -Identity James.Joyce -CustomAttribute9 "Beer"

Using the List

Using the dynamic distribution list is as easy as using any distribution list. The notable difference from an end user perspective is that there’s no option to expand the list and reveal the individual members by adding them to the message header (Figure 1).

Using a dynamic distribution list to address email
Figure 1: Using a dynamic distribution list to address email

The list membership is evaluated each time a message addressed to the list passes through the Exchange transport service and messages for matching recipients are generated at that point.

We’re rather fond of dynamic distribution lists, so they are covered in the Office 365 for IT Pros eBook. It’s an Office 365 feature that hasn’t changed in years… but we still like it.

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