Use this command
$Database= (Get-MailboxDatabase "Staff-Mail Store"). distinguishedName New-DynamicDistributionGroup AllStaff -RecipientFilter {Database -eq$Database} -RecipientContainer "OU=Users List,DC=MyDomain,DC=com"-OrganizationalUnit "OU=Exchange,OU=Distribution Groups,DC=MyDomain,DC=com"
Jasjit Singh Dhindsa | ITIL v3 | IASA Foundation Certified | MCITP:Exchange 2010 | Exchange 2007 | MCTS:OCS 2007 | Exchange 2010 | Exchange 2007 | MCSA:Messaging | Security | MCSE:Messaging | Security