My-Technet

http://technet.microsoft.com/en-us/library/cc164350(EXCHG.80).aspx

Add-ADPermission -Identity <name of distribution group> -User <name of user> -AccessRights WriteProperty -Properties "Member"

“There are multiple objects matching the identity “Group or Object name”. Please specify an unique value.

In this case, you’ll need to pipe a Get-DistributionGroup command into the Add-AdPermission command.

Get-DistributionGroup “doman.local/OU/Distribution Group” | Add-ADPermission –user “User or Security Group Name” –AccessRights WriteProperty –Properties “Member”