I want to create a new folder from within Mutt. I use Maildir format to store the folders on the machine I am running Mutt on.
(I also view the mail remotely using courier IMAP but this doesnt involve Mutt)
Edited to clarify role of IMAP
If Mutt cannot create maildirs directly, it is easy to do it yourself. A "Maildir" format mail directory has nothing special except for three subdirectories
Assuming that your mail is kept under
If you want a folder hierarchy "Archive" / "2010" / "06":
(Terminology: mail clients keep messages in 'folders', and the filesystem stores everything in 'directories'.)
I usually just save some email to new not-yet-existing folder, and mutt creates the folder for me.
For me it's pretty intuitive, as there is no point in having folder without mails in it, so I just create it by saving there first mails that should go there.