Install Exchange server productkey with PowerShell

This also works in Exchange 2010:

Set-ExchangeServer -Identity SR-XXXXX -ProductKey ABCDE-FGHIJ-KLMNO-PQRST-UVWXY

Or set all your servers at once: (This only works if all your Exchange server are the same version)

Get-ExchangeServer | Set-ExchangeServer -ProductKey ABCDE-FGHIJ-KLMNO-PQRST-UVWXY

After restarting the "Microsoft Exchange Information Store" the Activation will be effective. So to restart all Exchange Information Store services run:

Get-Service -Name "Microsoft Exchange Information Store" -ComputerName SR-XXXXX | Restart-Service