Exchange 2010 bug, the alias is empty. If your user is chinese name the simpledisplay name & smtp have question mark. You can use the below script to fix it.
$list=Get-Mailbox | where {$_.alias -like "???"}
ForEach ($item in $list)
{
$user=Get-User $item
$sam=$user.SAMAccountName
Set-Mailbox $item –Alias "$sam"
}
{
$user=Get-User $item
$sam=$user.SAMAccountName
Set-Mailbox $item –Alias "$sam"
}
This script help you to change question mark to SAMAccountName.
Do you have any question please contact me.