dired-bind-vmdired-bind-vm is a variable defined in `
dired-x.el'. Its value is
nilDocumentation: Non-nil means "V" runs `dired-vm', otherwise "V" runs `dired-rmail'. RMAIL files in the old Babyl format (used before before Emacs 23.1) contain "-*- rmail -*-" at the top, so `dired-find-file' will run `rmail' on these files. New RMAIL files use the standard mbox format, and so cannot be distinguished in this way. You can customize this variable.