How to List Members of a Dynamic Distribution Group
Dynamic Distribution Groups are a great feature of Exchange. You can easily use them to create a dynamic mail enabled group containing all of your users with mailboxes, or any other number of options. Since there is not a defined static list of members, it's slightly more difficult to get a list of all members. The two commands below, when ran from the Exchange Management Shell, will list all members of a Dynamic Distribution Group. These commands will work on any version of Exchange that support Dynamic Distribution Groups, including Exchange 2010, 2013, and 2016:
$e = Get-DynamicDistributionGroup "firstname.lastname@example.org"
Get-Recipient -RecipientPreviewFilter $e.RecipientFilter
It's important to note that a Dynamic Distribution Group, by it's very nature, is evaluated every time you query it, and could change from one query to another.