Exchange 2013 Import Distribution Group members from a CSV File

I am trying to import users (Contacts) with a CSV file.  The exchange server is setup with domain "company2.com" but we have contacts for users with "company1.com".

Currently we have a two email address for the users because we are in the process of moving to Exchange 2013.  So John Smith has and AD user account with John.Smith@company2.com and a contactJohn.Smith@company1.com.  All users have their mail being forwarded from company1.com to company2.com till we cut over fully.  But I need to make DL's with the contacts, I can not delete or remove any users or contact in the domain.  company1.com will still be our email address after we have migrated over.

Import-Csv C:\Temp\DL-Staff.csv | foreach {Add-DistributionGroupMember -IdentityDL-Staff -Member $_.identity}

CSV file has:

Identity,EmailAddress
John Smith,John.Smith@company1.com

When I run the powershell command I get:

There are multiple recipients matching the identity "John Smith". Please specify a unique value.
    + CategoryInfo          : NotSpecified: (:) [Add-DistributionGroupMember], ManagementObjectAmbiguousException
    + FullyQualifiedErrorId : [Server=exchange1,RequestId=XXXXXXXXXXXXXXXXXXXXXXXXX,TimeStamp=1/31/2014 4:11:5
   5 PM] E04A8CA0,Microsoft.Exchange.Management.RecipientTasks.AddDistributionGroupMember
    + PSComputerName        : exchange1

How can I create a DL with the contacts and exclude the AD users?  I don't want to do this in ECP because of the number of users to add.