Unix Mail Box
The nnmbox back end will use the standard Un*x mbox file to store mail. nnmbox will add extra headers to each mail article to say which group it belongs in.
Virtual server settings:
nnmbox-mbox-file
The name of the mail box in the user’s home directory. Default is ~/mbox.
nnmbox-active-file
The name of the active file for the mail box. Default is ~/.mbox-active.
nnmbox-get-new-mail
If non-nil, nnmbox will read incoming mail and split it into groups. Default is t.