After SP1, the security structure of exchange server has been improved. Exchange Server 2010 used shared permissions but now it uses split permissions. I will give you an example to understand what it is, A Exchange Server Administrator is able to manage its organization, it cannot manage other organization.
Ok, how to use new-mailbox command now?
1- Use split permissions and create user
2- If you say “I was happy to use shared permissions structure” let’s turn to old habits
a- setup.com /PrepareAD /ActiveDirectorySplitPermissions:false
b- New-ManagementRoleAssignment “Mail Recipient Creation_Organization Management” -Role “Mail Recipient Creation” -SecurityGroup “Organization Management”
New-ManagementRoleAssignment “Security Group Creation and Membership_Org Management” -Role “Security Group Creation and Membership” -SecurityGroup “Organization Management”
New-ManagementRoleAssignment “Mail Recipient Creation_Recipient Management” -Role “Mail Recipient Creation” -SecurityGroup “Recipient Management”
3- Restart the Server