spoolfile, folder, and 'y'

[list-user <info@xxxxxxxxxxxx>]

Hi all

Beside others I have the following lines in my muttrc:

set mbox_type   = "Maildir"
set spoolfile   = "/home/user/mutt_mail/inbox" 
set folder      = "/home/user/mutt_mail"  

mailboxes !
mailboxes = a
mailboxes = b
mailboxes = c


All mailboxes are put in the same directory: /home/user/mutt_mail/a etc.
By pressing 'y' I have 2 entries, '=/' and '=inbox'.
Actually I do want to see all my mailboxes, including the inbox.

How can I achieve that?
--
Thanks for your help.
Best regards,
Mike