Help with Powershell Cmd

Need Help with Getting an overview of all ActiveSync devices in the Exchange-organization in a Comma Separated Format.

I have been working with this but cant get the username format to run correctly

Get-Mailbox -ResultSize Unlimited | ForEach {
   #$user = $mailbox.DisplayName
   $deviceinfo.User = $mailbox.DisplayName
    Get-MobileDeviceStatistics -Mailbox:$_.Identity |
   Select-Object @{label="User" ; expression={$deviceinfo.User}},DeviceOS, lastsuccesssync
   
   
}

It just repeats the same user.

Thanks in advance