I personally don't use the Email client in the Archos, however I did try it just now. I can confirm this is a bug, however not really sure how to get emails to appear ... I'd use the web browser to browse my emails. Temporary solution, I know but I'm not really sure why it does that.
EDIT: There's another solution. I've noticed you can send emails effectively using gmail with it, only receiving is problematic. Thus, set it up to forward to some hotmail account you create(d), receive from that account, but send from gmail. It should, in theory, work. Again, I don't use the Archos for emails, however testing this seems to work, so ymmv.