Hove to move mail out of the C: drive

We have several computers that were configured at the factory: C: 2mb, D: 6mb, E: 12mb.
Most of the C: drives are woefully short of free space although most of the software have been installed on D. The mailbox alone is taking up 200MB of disk space and they can’t bear to part with their mail.
I tried changing the storage from C: to E: but the response time became unacceptable so I moved it back to C:
What is the best way of archiving mail to removable media? Copy the entire Inbox, Sent box, then delete stuff off of the current file?