Remember the basics when working with Dynamic Distribution Groups (I didn’t)

Overview:

I recently had a customer come to me with a simple issue of mail not being received in his Exchange 2013 environment when sending to a Dynamic Distribution Group he had just created. Well it certainly seemed like an easy issue to track down (which it technically was) but unfortunately I was a little too confident in my abilities & made the age-old mistake of overlooking the basics. Hopefully others can avoid that mistake after giving this a read.

Scenario:

Create a Dynamic Distribution Group named TestDL#1 whose membership is defined by a Universal Security Group named TestSecurityGroup using the following command in shell:

New-DynamicDistributionGroup -Name “TestDL#1” -RecipientFilter {MemberOfGroup -eq “CN=TestSecurityGroup,OU=End_Users,OU=Company_Users,DC=ASH,DC=NET”}

Note: This command places the Dynamic DL object into the default Users OU & also sets the msExchDynamicDLBaseDN to the Users OU’s Distibguished Name (CN=Users,DC=ASH,DC=NET). This will become important later.

I can verify the membership of this group by running:

$var = Get-DynamicDistributionGroup “TestDL#1”

Get-Recipient -RecipientPreviewFilter $var.RecipientFilter

In my case, the members show up correctly as John, Bob, Sam, & Dave. However, if I send emails to this group nobody gets them. When looking at messagetracking, the recipients show as {} (see below screenshot)

Now here’s the really interesting part. My security group, as well as my users are in the OU=End_Users,OU=Company_Users,DC=ASH,DC=NET Organizational Unit. However (as mentioned before in my Note), my Dynamic DL is in the CN=Users,DC=ASH,DC=NET Organizational Unit. Now if I move my users into the Users OU, then they receive the email & show up as valid recipients.

Now no matter which OU I move my Dynamic Distribution Group (TestDL#1) to, this behavior is the same.

For instance, if I had run the below command instead, I never would have noticed an issue because the Dynamic DL would’ve been created in the same OU as the users & the Security Group.

New-DynamicDistributionGroup -Name “TestDL#1” -OrganizationalUnit “ash.net/Company_Users/End_Users” -RecipientFilter {MemberOfGroup -eq “CN=TestSecurityGroup,OU=End_Users,OU=Company_Users,DC=ASH,DC=NET”}

The last head scratcher is if I move the actual AD Security Group (TestSecurityGroup) that I’m using to filter against to a different OU, I get the same behavior (no emails).

So it would seem that the solution is to ensure you always place the Dynamic Distribution Group into the same OU where ALL of your Security Group members are as well as the security group itself is.

This seemed crazy so I had to assume I wasn’t creating the filter correctly. It was at this point I pinged some colleagues of mine to see where I was going wrong.

Tip: Always get your buddies to peer review your work. A second set of eyes on an issue usually goes a long way to figuring things out.

Solution:

As it turned out, there were two things I failed to understand about this issue.

1. When you create a Dynamic Distribution Group, by default, the RecipientContainer setting for that group is set to the OU where the DDG is placed. This means that because I initially did not specify the OU for the DDG to be placed in, it was placed in the Users OU (CN=Users,DC=ASH,DC=NET). So when Exchange was performing its query to determine membership, it could only see members that were in the Users OU. So the solution in my scenario would be to use the –RecipientContainer parameter when creating the OU & specify the entire domain.

EX: New-DynamicDistributionGroup -Name “TestDL#1” -RecipientFilter {MemberOfGroup -eq “CN=TestSecurityGroup,OU=End_Users,OU=Company_Users,DC=ASH,DC=NET”} –RecipientContainer “ASH.NET”

This one was particularly embarrassing because the answer was clearly in the TechNet article for the New-DynamicDistributionGroup cmdlet.

2. The other thing I didn’t realize was the reason my DDG broke when moving the Security Group I was filtering against. It was breaking because I specified the Security Group using its Distinguished Name, which included the OU it resided in (CN=TestSecurityGroup,OU=End_Users,OU=Company_Users,DC=ASH,DC=NET). So by moving the group I was making my query come up empty. Now the first thing I thought of was if I could specify the group using the common name or the GUID instead. Unfortunately, you cannot because of an AD limitation:

“MemberOfGroup filtering requires that you supply the full AD distinguished name of the group you’re trying to filter against. This is an AD limitation, and it happens because you’re really filtering this calculated back-link property from AD, not the simple concept of “memberOf” that we expose in Exchange.”

So the important thing to remember here is to either not move the Security Group you’re filtering against, or if you move it, to update your filter.

Thanks go to MVPs Tony Redmond & Tony Murray for pointing these two important facts out to me.

Conclusion:

As I found out, a strong foundational knowledge of Active Directory is key to being a strong Exchange Admin/Consultant/Support Engineer. But even when you feel confident in your abilities for a given topic, don’t be afraid to ask people you trust. You might find out you’re either a bit rusty or not as knowledgeable as you thought you were J