I use offlineimap to pull down some Gmail mail stores. With offlineimap I use sep = / and nothing more exotic.

With dovecot I can see INBOX, messages, and messages in top level folders but not subfolders.

I'm dealing with folder structure that looks like this:

/opt/gmail/joe/Later /opt/gmail/joe/Tech/Projects /opt/gmail/joe/Tech/Projects/Fun /opt/gmail/joe/Tech/Projects/Failed /opt/gmail/joe/Tech/Projects/Planning

The folder Later has cur, tmp, new and I can see messages.

Projects is a container for subfolders Fun, Failed, Planning. I know Fun, Failed, Planning has messages but I'm not able to expand (via thunderbird) the folder Projects.

I have this configured in dovecot.conf

mail_location = maildir:/opt/gmail/joe:INBOX=/opt/gmail/joe/INBOX:LAYOUT=fs

namespace private { separator = / list = yes }

And this is what's getting logged...

dovecot: Feb 18 07:26:39 Info: IMAP(joe): Namespace: type=private, prefix=, sep=/, inbox=no, hidden=no, list=yes, subscriptions=yes

dovecot: Feb 18 07:26:39 Info: IMAP(joe): maildir: data=/opt/gmail/joe:INBOX=/opt/gmail/joe/INBOX:LAYOUT=fs

dovecot: Feb 18 07:26:39 Info: IMAP(joe): fs: root=/opt/gmail/joe, index=, control=, inbox=/opt/gmail/joe/INBOX