I am working with a hosted Exchange 2007 server and Outlook 2003. For some time when operating in chached exchange mode there has been an issue with emails that were sent not appearing in the sent mail folder. This problem has persisted through migration to a brand new workstation, and through the migration from one host on exchange 2003 to another host using exchange 2007. In the prossess of diagnosing this error we took the user off of chached exchange mode and the problem no longer occurred.
In speaking to the tech support at out exchange host it has been suggested that the issue is most likely on the local system, on the workstations in question.
The systems in question are using Windows XP Professional (all up to date), Trend Micro Office Scan as the anti virus protection, and PGP Universal Satalite for encryption.