Get-MessageTrackingLog -Start -EventId submit | fl Sender, sourceContext MOMT is Outlook and the other two speaks for them self. It actually is possible for an admin to tell if a message was sent from Outlook or OWA by looking at the MessageTracking and the information in Naren Neelam, Messaging Consultant, ITBigBang (P) Ltd | Hire Us for Messaging Consulting
I think there is no possible way to check if the mail is sent was from Outlook or OWA.
