get distribution list from gal

If I correctly understood your problem, a distribution list is the same as any other e-mail address. So you can use the same class which you are using it for individual emails.

or do you mean this?

using Outlook = Microsoft.Office.Interop.Outlook;

private void GetDistributionListMembers()
{
	Outlook.SelectNamesDialog snd =
		Application.Session.GetSelectNamesDialog();
	Outlook.AddressLists addrLists =
		Application.Session.AddressLists;
	foreach (Outlook.AddressList addrList in addrLists)
	{
		if (addrList.Name == "All Groups")
		{
			snd.InitialAddressList = addrList;
			break;
		}
	}
	snd.NumberOfRecipientSelectors =
		Outlook.OlRecipientSelectors.olShowTo;
	snd.ToLabel = "D/L";
	snd.ShowOnlyInitialAddressList = true;
	snd.AllowMultipleSelection = false;
	snd.Display();
	if (snd.Recipients.Count > 0)
	{
		Outlook.AddressEntry addrEntry =
			snd.Recipients[1].AddressEntry;
		if (addrEntry.AddressEntryUserType ==
			Outlook.OlAddressEntryUserType.
			olExchangeDistributionListAddressEntry)
		{
			Outlook.ExchangeDistributionList exchDL =
				addrEntry.GetExchangeDistributionList();
			Outlook.AddressEntries addrEntries =
				exchDL.GetExchangeDistributionListMembers();
			if (addrEntries != null)
				foreach (Outlook.AddressEntry exchDLMember
								in addrEntries)
				{
					Debug.WriteLine(exchDLMember.Name);
				}
		}
	}
}

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Thanks for your reply.

I was hoping to stay away from the outlook intrerop stuff as we have multiple versions of outlook but...

I tried using your code example and receive the compile error:
"  The name 'Application' does not exist in the current context  "

I have added the following .net reference:
C:\Program Files\Microsoft Visual Studio 9.0\Visual Studio Tools for Office\PIA\Office12\Microsoft.Office.Interop.Outlook.dll

perfect!  Is there a way to do this against Active Directory without having to use the interop dll?