I don't even know where to begin with this. The user has a Windows 7 (x32) system running Outlook 2007. It is part of an Windows 2003 SBS domain (single server) with Exchange 2003. When she tries to send email, Outlook reports that the message was sent. The recipient never gets it.
I found from looking at the message tracker in System Manager that the Exchange server is trying to send it under someone else's username. It is then bouncing back to that user because the original user doesn't have "send as" privs.
I've tried creating a new profile. I tried removing and re-adding the PC to the domain.
If she uses OWA or Outlook on another PC, everything works fine. It is only on this on PC.