Multiple incoming folders
If you have a more advanced setup by using "procmail" or something similar so that your incoming emails are automatically sorted into separate folders, then you can inform mutt about where to look for new mail by means of the "mailboxes" command. You can use "mutt -y" to start up with the list of incoming folders. Within mutt you can toggle the folder-browser view between regular folders and "mailboxes": enter folder-browser with "c?", then hit "TAB" (the default for "toggle-mailboxes" function, hit "?" again for actual key-binding). More on this later.
You can save a lot of typing if you have many "mailboxes" entries, see MuttFaq/RemoteFolder.