A user needed a distribution list, so that she could send a message to 2000+ users. Doing this in Exchange meant that the message would not be duplicated 2000+ times, but the information on the users was in a .csv file.
Using the following command, I was able to add the users to an empty Distribution Group:
Type C:\jjlist.csv | ForEach-Object -Process {Add-DistributionGroupMember -Identity “nameofyourlist” -Member $_}
This works where all users you wish to add to the group exist in the AD, and where you have first made the Distribution Group in Exchange.