User has iMac with latest Yosemite 10.10
Email is on an Exchange Server at Intermedia, accessed through ActiveSync.
Exchange mailbox is greater than 15 GB, mostly because of lots of photos that have been emailed over time.
Intermedia support recommends against having an Exchange mailbox larger than 5 GB, and suggests archiving old mail.
How can I implement a system of small Exchange mailbox, yet still have connection to archives and use the Apple Mail program?