Today I had an AD administrator create a distribution group and add all the members to it in Active Directory. They needed it enabled in Exchange so I thought easy just go into the EAC (Exchange Administrative Center) and add an existing group. This was the case in Exchange 2007 and 2010 but not in 2013. In order to add an existing group so you don’t have to recreate it from the EAC and add all the users back you go into EMC (Exchange Management Console). Then once in Powershell type in the command below.
Enable-DistributionGroup -Identity “groupnameinAD” -Alias “groupname” -DisplayName “displayname"