Why not just write a small routine that tests the folder to see if there's more than x number of emails, and if so, moves the excess to a series of secondary folders, each of which can then by loaded without problems? I assume your objective is to filter the catch-all email and move the good messages to a different place, so separating the catch-all into several locations temporarily probably won't cause trouble.

This would be classified as the "easy" way out. I know programmers love to do things the hard way.