Giving SendAs permissions to a distribution Group

Once you have created a distribution group, if you need one user to have sendas permission then do the following in exchange powershell

Set-DistributionGroup GROUPEMAILADDRESS@domain.com -GrantSendOnBehalfto USER@domain.com

to set a multiple group use the following

Set-DistributionGroup GROUPEMAILADDRESS@domain.com -GrantSendOnBehalfto @{Add="USER@domain.com", "USER2@domain.com", "USER3@domain.com"}

to check who has access

Get-DistributionGroup GROUPEMAILADDRESS@domain.com | fl name,grant*