|ReplyAll alerts you before unintentionally replying all, or if you are a confidential BCC recipient of the e-mail.
You cannot directly add a distribution list to another one. So a detour via a MailItem is necessary: We add an existing distribution list (current folder selection in this sample) as a recipient to an e-mail. Then we can get the list back via the MailItem's Recipients collection and add that one to a second distribution list.
Public Sub CreateNestedDL()
Dim DL As Outlook.DistListItem
Dim Mail As Outlook.MailItem
Set DL = Application.ActiveExplorer.Selection(1)
Set Mail = Application.CreateItem(olMailItem)
If Mail.Recipients.ResolveAll Then
Set DL = Application.CreateItem(olDistributionListItem)
DL.DLName = "test item"