Members of a dynamic distribution group in an Exchange hybrid deployment don't receive email messages
Original KB number: 3061396
Symptoms
You have a hybrid deployment of Exchange Online in Microsoft 365 and on-premises Exchange Server. In this environment, certain members of a dynamic distribution group do not receive email messages. Senders also do not receive a non-delivery report (NDR). However, if a sender manually adds the user to the To field of an email message instead of sending the message to the distribution group, the message is delivered to and received by the user.
Additionally, if you run a command such as the following to return a list of recipients in the dynamic distribution group, the user doesn't appear in the list:
$list = Get-DynamicDistributionGroup sales@contoso.com
Get-Recipient -RecipientPreviewFilter $list.RecipientFilter -OrganizationalUnit $list.RecipientContainer
Cause
This problem occurs if the dynamic distribution group was set up before the environment became a hybrid deployment and if the dynamic distribution group uses filters to include only mailboxes. Mailboxes that are migrated to Microsoft 365 become mail-enabled users in the on-premises directory.
Resolution
Use the Set-DynamicDistributionGroup cmdlet to update the filters for the dynamic distribution group to include mail-enabled users. For example, run the following command:
Set-DynamicDistributionGroup -Identity sales@contoso.com -RecipientFilter {(RecipientType -eq 'UserMailbox') -or (RecipientType -eq 'MailUser') -or (RecipientType -eq 'MailContact')}
Important
When you add filters to an existing dynamic distribution, be sure to include the existing recipient filters. Why? The Set-DynamicDistributionGroup cmdlet replaces the existing recipient filters with the value that you specify. Also, you don't need to specify the default recipient filters. Exchange will add these filters automatically.
More information
For more information, see Get-DynamicDistributionGroup and Set-DynamicDistributionGroup.
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