Selam Mseyda
$FixAutoMapping = Get-MailboxPermission sharedmailbox |where {$_AccessRights -eq "FullAccess" -and $_IsInherited -eq $false}
$FixAutoMapping | Remove-MailboxPermission
$FixAutoMapping | ForEach {Add-MailboxPermission -Identity $_.Identity -User $_.User -AccessRights:FullAccess -AutoMapping $false}

kaynak : Disable Outlook Auto-Mapping with Full Access Mailboxes: Exchange 2010 Help

Test etmediyseniz üstteki kod bloğunu test edermisiniz ?