Get-messagetrackinglogs MessageSubject [Undisclosed]

Hello Guys,

How do you think I get the actual message subject when running the Get-MessageTrackingLogs. I'm getting [Undisclosed] from the result.

Timestamp    MessageID  MessageSubjectClientHostnameEventId
30/04/2015 06:03<c3f7e127630e451ca837211c37de979d@xxxxxxx.net>[Undisclosed]xxxxxxxxxxxDELIVER

Thanks!

BR,
Uddan