Interesting - it seems that all the folders in Maildir are named with semicolon separators. For example ";INBOX". If I change the semi-colons to fullstops and ensure that the permissions are correct my email client sees the folders and files ...
I'm going through the same process, and noticed that:
a) None of my IMAP sub-folders contains mail
b) The [empty] sub-folders contained semi-colons in my mail client
c) Folders that originall contained full stops (e.g. my 'contribs.org' folder) got split into sub-folders (e.g. contribs->org)
So, given those 'clues' I am also thinking of changing the semi-colons to full stops. A quick question: did you change ALL the semi-colons, or did you leave the initial (e.g. ";archive;2002" to ";archive.2000" or ".archive.2002")? I suspect the initial semi-colon should be left, but I'm not sure.
Is this a general problem for all upgrades 6.0.1->7.x, or is it related to specific contributions? I can't find anything in the bug tracker, which makes me think it is not a general problem, but perhaps no-one has tested migrating a complex structure of IMAP folders yet?
Any hints appreciated (and I'll raise a bug if it looks like it is one).
-- JJ