Some iPhones can have a problem with some Exchange servers due to the fact that they are not fully manageable using ActiveSync Policies. The New-ActiveSyncMailboxPolicy commandlet is can be used with the -Name parameter to assign a name to the new ActiveSyncMailboxPolicy, which we’ll call iPhone. To allow devices that are not fully manageable to use ActiveSync, an ActiveSyncMailboxPolicy needs to be created where -AllowNonProvisionableDevices is set it to $true. For example, if we were to create such a policy and call it iPhone we would use the following command:
New-ActiveSyncMailboxPolicy -Name iPhone -AllowNonProvisionableDevices $true