I've got huge amounts of old e-mails which begin to clutter my IMAP mailbox. I can easily download them all from my account and store them as .mbox files locally, but the question is: How can I browse them after storing them locally? I need to search through them (more or less efficiently.), and occasionally open an attachment. They will be never synchronised again with an online folder. I also don't need the ability to resort/delete/retag etc.
Try this: Importing "mbox"
It gives you instructions on how to import local mbox files into a few different clients. You will then be able to view them.