To trap when a new item is delivered or sent you would need to be running an
ItemAdd and/or Application.Send event handler. That would give you an
immediate event.

Or you could iterate all teh folders you are interested in and maintain a
list of items for each folder. At intervals you would then iterate the
folders again to see what's new.

You don't mention your knowledge of programming Outlook or which version of
Office you're using but you might want to start out by looking at
www.outlookcode.com for lots of sample Outlook code.