Subfolders of INBOX with altnamepsace

[Paul Fisher]

We're in the process of migrating from an IMAP server that uses a
namespace equivalent to the Cyrus altnamespace but in addition
supports storing subfolders under INBOX.

Considering the number of users we currently support, we're
considering modifying Cyrus to support such a setup.

Such a change would likely result in an extra config option permitting
subfolders of INBOX when using altnamespace, and once an installation
uses that option and subfolders of INBOX are created, switching back
to the standard namespace would either not be possible or would at
least be somewhat disruptive.

I'm not aware of any existing patches that accomplish this sort of
behavior.  If we were to make these changes, would they be of use to
other sites, and would such a design change be considered for
acceptance upstream?

Paul