Not clear what you want to do "moving subfolders directly under the mailbox". Not clear either what you mean with "performance".
But - given this uncertainty - I don't expect any significant change. However, since moving is easy to undo, why not try and tell us?
Kees
for users w/outlook 2007 connected to exchange 2003/2007 and having 20 to 25 subfolders, w/ hundreds of emails each, will creating subfolders directly under the mailbox or moving those subfolders directly under the mailbox, improve performance? Either way, can you provide a reference for this?

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