Forwarding hunt group calls to a group voicemail

During a deployment, we were met with the request of calls in a hunt group (or queue) should be able to go to an Exchange UM enabled mailbox for the department/function.

HG name is department@sipdomain e.g. test@kml.local
Exchange mailbox is department@sipdomain e.g. test@kml.local
UPN for the Exchange mailbox is the same as the e-mailaddress

The mailbox account is (should be) disabled in AD, so first move is to enable the account. Then I enable the account for Lync using Powershell:
Get-CsAdUser -Identity "test@kml.local"|Enable-CsUser -RegistrarPool Lyncpool.kml.local -SipDomain kml.local -SipAddress sip:vm.test@kml.local

The Lync user should be Enterprise Voice enabled to be able to utilize the UM mailbox
Set-CsUser -Identity test@kml.local -EnterpriseVoiceEnabled $True

Next step is UM enabling the mailbox (implies that a UM Mailbox Policy has already been defined) this could be done using the Exchange Control Panel or Powershell:
Enable-UMMailbox -Identity "test@kml.local" -UMMailboxPolicy UmPolicy1 -Extensions 2000 -PIN 13579 -SIPResourceIdentifier "test@kml.local"

Now we'll use SEFAUtil to set the Lync forwarding destination for test@kml.local.
.\SEFAUtil.exe /server:lyncpool.kml.local test@kml.local /enablefwdimmediate /setfwddestination:"sip:test@kml.local;app=voicemail"

Now we can assign the Forward to Voicemail destination in the HG setup and don't forget to record a greeting in the Exchange mailbox.

After recording a greeting, you should consider disabling the AD account again. If you decide to disable the account, the users of the mailbox cannot record a new greeting unless an administrator (you) reenable the account again.