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 accounts for {0}% of this user's RPC processor usage. Typically, this operation is very expensive. It does not usually indicate a problem.