mbx format is not such a format; nor is traditional UNIX mailbox format.
The dual-use mailbox formats supported in the distribution version of c-client are mh, mx, and news.
Personally, I think that "dual-use" is a bad idea from a user interface point of view, since that means that for a name you have to have a separate "open as mailbox" and "open as directory" operation. But this seems to be a matter of religion.
-- Mark --
http://staff.washington.edu/mrc Science does not emerge from voting, party politics, or public debate. Si vis pacem, para bellum.
