1. Start Outlook in safe mode. (No, not Windows Safe mode.) If that helps, look at what addons are present and remove them.
2. Even the Sent folder can have a VIEW applied. Check the view as well as the setting to save such in the Sent folder.
Bob
A friend of mine has a Dell laptop running Vista and Outlook 2007. He is experiencing problems with Outlook. Here is what he told me...
" When I start the program,
it gives me a message indicating that the program will not start because
of an error, unidentified, to close Outlook and Windows, and then
restart the computer and reopen Outlook. When I do that, I still get
the same response. However, the program will open, I can send and
receive messages, but nothing appears in my "Sent" box."
Does anyone have some thoughts on what is going on and how to resolve it? I'd appreciate it.

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