Mal,
Just for poops and giggles, I tried the Tweaks2K hack to move the mail storage to the SD card. This does create a "Mail" folder in the SD card with what seems like all of the needed goodies. Alas, the cemail.vol stays where it is. I did read a couple posts that suggest renaming it if it becomes corrupt. After you rename it (or just delete it) Windows creates a brand new shiny one!