Event 1016 Generated When You Open Mailbox or Schedule of Another User

When you attempt to access another user's mailbox or schedule, Microsoft Exchange generates the following event in the Application Event log: This occurs even if you have permission to access the mailbox, and it occurs regardless of whether your attempt is successful or unsuccessful.

This behavior is by design.

Exchange records Event 1016 in the Event Log regardless of how you set the diagnostics logging level on the Information Store.

The decision to log this error was made with security in mind. It is important that any possible security breach be logged. If this type of logging were suppressed, an actual breach of security would not be logged.