Outlook - occasionally receiving email notifications for someone else

Outlook 2010/Exchange 2007
 
This is bizarre. Now and then I receive random email notifications addressed to someone else. I can open the message if I click on the notification, but as soon as I close it it disappears and is not in my inbox.
 
I am not a delegate for this person, I have no connection to them except we work for the same organization. A bit worried incase someone else gets emails addressed to me in the same way.
 
Any ideas?
 
Thanks in advance