I use mutt to read mail locally but mutt is not configured to use the Maildir format "out-of-the-box".
I found this guide useful, but it still doesn't quite work with qmail because qmail doesn't deliver mail to super-users (e.g. root). Typically, root mail is delivered to the alias user by creating a .qmail-root file in the alias user's home directory.
So, to tell mutt about this I added the following lines to ~root/.muttrc:
set folder="~alias/Maildir/" set spoolfile="~alias/Maildir/"