Subfolders are Maildirs starting with a dot in the toplevel Maildir, to designate a subfolder being inside another subfolder, prepend that other subfolders name to it. This leads to a layout that looks like this:
Maildir/ cur/ new/ tmp/ .Mutt.dev/ cur/ new/ tmp/ .Mutt.users/ cur/ new/ tmp/ .Sent cur/ new/ tmp/
Besides the INBOX there's a Sent folder and the (virtual) Mutt folder which contains both the users and dev folders. Accessing this through an IMAP server with some GUI MUA would show a tree like that:
INBOX |-Mutt | |-dev | `-users `-Sent
#!comment http://www.flounder.net/~mrsam/maildrop/maildirmake.html broken
Compatible implementations of maildirmake as shipped with Courier, dovecot and maildrop for example allow for easy creation of subfolders.
Information about kmail
Apparently, ExtendedMaildir implementation is different for kmail 1.7.1. This information should be important if you use getmail or fetchmail and to use several mailer. For the same tree, it's look like :
Maildir/ inbox/ cur/ new/ tmp/ .inbox.directory/ Mutt/ cur/ new/ tmp/ .Mutt.index .Mutt.index.ids .Mutt.directory/ dev/ cur/ new/ tmp/ users/ cur/ new/ tmp/ .dev.index .dev.index.ids .users.index .users.index.ids sent/ cur/ new/ tmp/
It would be useful to have a good RFC for maildir ...
Can the mutt file browser be configured to display .Mutt.dev and .Mutt.users as a folder named Mutt containing mailboxes named dev and users?