The Exchange Server User Monitor (ExMon) RPC data indicates that the user '{3}' is performing a costly MAPI operation "{4}". ...

The Exchange Server User Monitor (ExMon) RPC data indicates that the user '{3}' is performing a costly MAPI operation "{4}". This operation accounts for {0}% of this user's RPC processor usage. If this operation is seen in conjunction with the MAPI operation 'QueryRows', in may indicate that the client is requesting a large number of items, or a large number of properties for each item. It is normal to see high cost in this operation in conjunction with 'MoveCopyMessages', 'DeleteMessages', or other bulk MAPI operations.